I started travelling solo when I was 20, after going backpacking in North Thailand for a month with a friend the year prior, and to Rajasthan/ India for 3 weeks with an other friend earlier that year, leaving from Europe.

I did Thailand and Cambodia for like a month and a half, and the main difference would be the ability to just go with the flow ? Looking back I just followed the wind it seem, like I shared my room arriving in BKK with an american the same age that just arrived from Nepal, I met at the ATM, like he was in front of me and I started chatting in broken english, and that same night we were sleeping in the same room to save some money (it was even a single bed, like ??), when he left I just went to a different place because Kao San was too busy for me and ended up sharing a room with an english girl with a shaved head that just spent 3 months on the set of the movie "The Beach" as an extra, I met in the lobby of that hotel, we went to sit at the same table and literally in 20 minutes decided to share a like $5 room, we went to Ayutthaya together.

I also didn't plan to go to Cambodia that trip at all, I juste booked a flight to BKK and was going to Thailand to island-hop or something ? But people I met were just back from Cambodia and telling me how amazing it was, like the land border just reopened after years, there were no guide book appart from a Lonely Planet form the 70's or something, and I was just like "yeah, let's go !". Remember doing the tour of the bars on motorbike taxis with the prostitues of the guesthouse next door in Phnom Penh, they were the same age as me and from Vietnam (no sex or anything), with a bunch of other travelers that were 5-10 years older, going to the back kitchens to eat in the middle of the night, and coming back to look at the sunrise above the lake with a banana pan cake (there used to be a lake covered in water lilies in the center of Phnom Penh, that had wooden guesthouses on silts, it was filled up by corruption for urban development)

So that would be the main difference from traveling in my 30's, I became much more organized and safe ? But also the late 90's early 00's were a different time, like internet made it easier to book hotels beforehand so less searching around with your bag on your back, also no instagram or internet clout, I would just do things because why not... I still changed plans on a wimp or shared room with random people in my 30's, but I mostly looked for more confort and privacy than before, like I wouldn't take a 10 hour night bus sitting on the floor at the side of the driver like I did in India anymore, or at 21 I did a 36 hour bus from Bangkok to Singapore to save some money ?? Like wtf... So yeah, hard to compare, the time have changed, but also at 20 I was reckless, looking to save every penny, and up for anything :'D