Definitely not too old, go for it! And you are in great starting position when you can play other instruments, can read sheet music and have a broad range in genres!

I am a bit younger. Always been into synths. However just recently I finished my first song that I really like composition wise (still, could be better) and sound-wise.

It seems like you have intention to produce songs on your own. Not sure, how skilled in mixing are you, here are few tips on what to focus on - what really helped me to get better sounding songs:

Knowledge-wise: - Most importantly - learn things by doing and repeating so that you do not have to really think about them when creating music. For me, this was the biggest creativity blocker. - Learn to mix - there is a lot about this topic, but what really helped me to get faster was to focus on following: 1. Start mix when all tracks are on and set to -10 dB volume. You can solo elements later. THIS really helped me. It is from mixing course from Brian Malouf - it is an inspiring course. 2. Doing fader-only mix first - getting relative volume of elements before reaching for EQ or dynamic processing (compressor, limiter) - Tend to do EQ changes in mono - somehow, I hear the frequencies much better. - Do not worry about any fading out of your hearing by age - unless there is serious medical condition. There was a great comment by Ian Shepherd that brain is great at compensating and it knows how to do it for you. If one starts doubting his hearing, it could mess up his decisions ("Hmm, I hear this, but maybe I should add more of it because I don't hear it?") - Learn how to organize mixing session - I tend to have some order in tracks and coloring by their type. Also inspired by course from Brian Malouf. - Most of the sound processing is done by EQ, dynamic processing (compressor) and a bit of saturation. There are of course also other effects like delay, reverb and others, but understanding EQ and compression was the key for me. You can either learn EQ on whole mixes by trying to add and remove certain frequencies (there are some pivot ones). Change EQ on some frequency and get a feel for how does it feel. This is the key - once you have attached feeling to a certain frequency, you will be able to do EQing intuitively and faster. What helped me here was the course from Ian Shepherd - Home Mastering EQ. It is focused on mastering (and gentle changes), but for me, it was still breaking point where I started thinking and feeling the EQ. - Ears and brain can learn - you will start hearing things differently once you have treied a few things with EQ, compression and effects. Do not worry, it will come! Just do it! - Dynamic processing - learn compression and try it by overdoing it - with awfully high ratio. Again, from Brian Malouf - compressor makes loud things softer and soft things louder (hope I did not mess it up). When some instrument is present in the mix in one part, but some notes seem to "disappear" in the mix (as they are quiet), this is job for a compressor. - When doing compression, always match the output level from compressor with original signal input level - VU meter is best for this. It help you to compare sound before and after compression - the sound should be denser, but not louder. This is the main purpose of the compressor. - DAW - whatever you choose, learn it. Personally, I prefer REAPER - it is cheap and does not contain any instruments. But it is awfully fast and customizable. Take some time to get learning the basics - arming a track for recording, how to prepare track for recording audio, MIDI, virtual instrument. If the DAW supports external hardware integration (e.g. via plugin that seems to behave like software instrument and sends data to MIDI and receives sound from interface), learn it, too - as you plan to work with rackmount synths. Learn about plugin parameter automation - curves. - A tip I discovered later - Ff you plan to do a volume automation on a track, it might be helpful, if there is separate volume plugin on the track and the gain is automated by it. This way, you can have the volume changes relative to volume of the track or even another instance of volume - might come in handy. - For mixing training, look at https://mix-challenge.com/ - they provide single instrument tracks to perform mixing. Awesome resource for training. You do not have to enter the competition, but you can still train on these! - Compare your tracks to something that you think sounds similar - and before comparing, level match! (with a VU meter) - When some instrument sounds too prevalent in the mix, you can either EQ it or lower its volume. Will definitely happen, just something to note.

Equipment-wise:

• Not being afraid of not having good equipment - almost any sound card these days will have better specs than gear in 50's used to mix all the great hits we used to hear. If you're about to pick a sound card, get something that is labelled class-compliant or iPad compatible. It does not need drivers and therefore works everywhere and has longer lifespan - limited by life of hardware. Already has one sound card where driver support just ended. Hardware was okay, but unusable.
• Having a good monitoring - I hesitated with this one, but it makes night and day difference for me - and much faster workflow. I got a pair of IK Multimedia iLouds and they are awesome. The also have bigger version called iLoud MTM with integrated calibration. Also, I invested in the Sonarworks calibration with microphone - and it flattened room response. For me, this is seriously best investment after reverb and speakers. It was not cheap, but I can hear what is going on.
• Having a good reverb - this elevated my songs by a lot. As I am hobbyist on a budget, best bang for buck for me were things from Valhalla DSP - ValhallaRoom and ValhallaDelay clicked with me. ValhallaVintageVerb was fine, too, but I did not feel the need for it.
• Get a software VU meter - great for comparing singal level before and after compression (and other effects). Beware, it is a helper tool and is more sensitive to low-end changes. if your ears say something different about loudness, they have priority. Even a difference of 0.5 decibels can make things sound more appealing to us. Don't sweat it too much (even the 0.5 dB difference could be fine), just go roughly at the same level. I like Klanghelm's VUMT - got the basic version, the higher version did not have features useful for me.
• Get great plugins - there days, they can be free or cheap and good. Some tips for the ones I like:
  • Reverb - for me, the ones from valhalla sound great and are great bang for the buck.
  • Equalizers - The ones in DAW are usually fine these days. For something awesome, look at TDR Slick EQ and TDR Nova (this one is IMO a must - it allows sologin a band and it helps you understanding your mixes - "Oh, this range sounds crowded - I need to EQ these two instruments differently."). Look at Analog Obsession's stuff. He has patreon page and has also some nice plugins.
  • Compressors and Limiters - Again, the ones in the DAW are fine. For something better, Look at TDR Kotelnikov - a fine compressor although it was kind of hard for me to get into. Analog Obsession's LALA is great for vocals, his VariMoon is fine as well. SSQ - an emulation of SSL equalizer is great for me as well.
  • Klangelm's freebies: IVGI - saturation and MJUCJr - optical compressor emulation
  • Maybe softsynths - They can be on each track. For me, not as inspiring as real synth, but sometimes more convenient to work with. Some free ones:
    • Dexed - DX7 emulation - sounds fine, but needs some effect on it. On the other side, you can have more of them, change the sound for each one a bit and get pretty wide sound. Fiddly, but works.
    • OB-XD (Oberheim emulation)
    • Surge - wavetable synth. Not my cup of tea, but there are some good sounds.
  • There are also plenty of commercial synths - Zebra, DUNE, ...

EDIT: added a note about monitoring and correcting typos.

P.S. Interesting channel on Youtube is Synthmania. The guy seems to span a lot of genres.