Get a decent set of exercise bands. I have 5lbs all the way up to multiple 100lbs ones. They are relatively cheap, light and highly mobile.

Military Service. I just don't have to pay for pain meds and I still get to fall apart over time!

Try not doing any stupid things that'll harm the body more.

I'm 45 and topfit. If you really feel like you're declining at 30 you've never taken care of yourself. What makes you think you can do it now?

Preferably to remain steady: Eat a varied (mostly) plant based diet. Work up a sweat at least 3 times a week and do some light movement everyday for 30 minutes. You don't need to do anything crazy, you don't need to fucking start pumping iron, you don't need to become a protein bro. Just find 30 minutes a day and stop eating food that you already know is bad for yourself. Especially not too much.

And fucking go to a doctor when your joints hurt or it takes you 5 time's longer to heal. It's not normal. Stop normalizeing being unhealthy.

You are 30-something and you feel over the hill.... Ok...

Your joints should be optimal at that age so I have no idea whats going on. Are you American eating fast food a lot? I dont know otherwise what can cause that...