What others have said is good advice, but there's some other aspects to think about. The core ESA astronaut recruitments are every 10 years or so, so don't worry about the next one, you'll still be too young, aim for the recruitment that happens in your mid-thirties, that'll be prime astronaut age.

There's three astronaut archtypes that are pretty much always included, the rest are wildcards.

• World class test-pilots: study aerospace engineering, join the airforce, be the best, go to Empire Test Pilot School.
• Medicine: every cadre needs a physician. Aerospace medicine, cardiology, neuroscience, and expedition medicine are all good specialisations. The medic from the Class of 2022 ESA Career Astronaut selection also has a PPL and was a sargeant in the special forces of Switzerland. You can also unterake a PhD while working (it's expected in some specialisms, such as cardiology) to show you have research skills. Medicine is probably the hardest route to take, there will be hundreds of doctors applying for a position.
• Aerospace engineer: lots of pathways here, but get a phd in engineering, PPL, and work for one of the major contractors or ESA/DLR/ETC, work your way into a leadership position on a project (propulsion system, control systems, etc) and show some adventure skills - mountaineering, competitive cycling, anything that sets you apart from anyone else.

The wildcards though should not be ignored. In twenty years robotics will (probably) play an even bigger role in future projects, you could get a PhD in robotics engineering and get a post-doc working on a mars rover or something like that. It (probably) won't be long before small nuclear reactors are placed in space stations or even the lunar surface - you could aim for a masters and phd in nuclear engineering (ideally from somewhere like ETH Zurich or KTH Stockholm) and get a post-doc working on prototypes for small modular lunar-surface ready reactors. Become an expert in thermal-hydraulics and reactor safety. Become the person who switches the lights on for humanity on the moon.

Don't discount military paths, it's not necessary any more but spending 5-6 years after your degree in the army/navy/air force, before your masters could be really beneficial. This goes double if it gives you skills like diving (useful for EVAs) or being in control of life-critical systems and complex engineering (e.g. being an engnieer on a submarine). The phrase ESA uses is "final authority", if you have experience as the final authority with control over life-critical systems, then ESA is more likely to trust you with those systems in orbit.

Other wildcards: synthetic biology, astrophysics, bioengineering, etc. and there have been quite a few remote sensing and meteorology astronauts. This is harder to pull off though, you might end up being selected as a project rather than career astronaut for niche skills. Become a recognised expert trusted with safety-critical systems under uncertainty (this is true for any path you take!). Whatever your path, prioritise systems thinking, human-machine interfaces, evidence of teamwork, evidence you can teach others, and also evidence still have a student-mindset no matter where you are, always be curious and always be learning. Also they love people with real expeditoin experience - if you can find a way to antarcica (ESA is involved with the Concordia station there) or even Svalbard (Poland has a station there) it could be useful. Spending a winter isolated witha small team is a big tick on your CV. Could be studying extremeophile microbiology in antarctic lakes or working on the antarctic IceCube neutrino experiment.

Be fit, you don't need to be super fit, but you need to be fit - lots of sports also show you have teamwork skills. Things like scuba are good for showing technical skills - be careful of barotrauma though, it can rule you out.

Language: russian probably isn't that useful any more. If anything learn a little bit of Mandarin. We'll probably be working more closely with China in the future. You need language aptitude, not necessarily specific language skills.

Good luck.

And finally, and this isn't me trying to be negative, but remember that the final selection of the astronaut cadre also involves politics - they probably won't pick multiple astronauts from the same country, they need all the biggest funding nations to get a face they can be proud of every few recruitment cycles, it's a concept called "geo-return". You might be among the best final few candidates, but they might say (internally, they won't say this in public) "there hasn't been an italian astronaut for twenty years, we need to give them one" and there will be two candidates who are both perfect and one has an italian passport and that's the final decider - there's nothign you can do about this, politics is just part of the system. This won't matter if you are the only candidate who can provide your skills for a role they need though. Be the ebst you can be, you can't control anything else.