welcome kitesmurf!
Its funny because i started riding again when i turned 30 haha. Are there legit bike trails close enough that you can visit multiple times a week? And are these trails beneficial to a mountain bike? roots, rocks, steep descents etc. Or are the trails youll be visiting more or less dirt roads? Cause thats a good determinant of what you should invest in as well.
I purchased a hardtail gary fisher piranha with modest componentry and though it made me better, i felt beat up at the end of all my rides. But that was probably my conditioning. I found the more i rode the more i realized what i wanted based on my style of riding. I rode a friends full suspension and i realized that even on just the flat lands and non-gnar terrain it was a more enjoyable ride.
So here i am one season later with a new to me full suspension frame and some upgrade componentry. Luckily some of the more expensive parts (shocks, wheelset and brakes) were ok enough for me to use this season. I’ll upgrade those parts as they break (more, haha) but it helped make the overall purchase price of my fisher and my new bike build significantly cheaper than what a similar bike wouldve costed new.
Then again you can get a real cheap bike now, get out on the trails and see how it suits you and then upgrade or buy another bike down the road. Just from my experience if i had had the loot i wouldve gone for a higher end but not highest end bike at the start.
What bikes were you looking at?