i'm 37 now and i still learn tricks. i was never really good tho, so i have lots of room to improve even basics. there's only a few tricks that now make up my core bag of tricks though, and keeping everything else is a real struggle. it always seems like i can't have it all. if i finally manage to learn inward heels, i lose some other trick. i don't really skate frequent enough to progress anymore anyway. i can't say at what i age i stopped progressing. i think as long as you skate regularily, if not frequently, you can progress at stuff you actually try. you can always try to manual longer, try to focus on that fliptrick you almost had a hundred times, but never nailed. but as you age and aren't able to skate as much due to health or work or family, you can't progress on all fronts anymore. you might still progress at manuals because you skate a manny pad for hours, four times a week, but your gapskills diminish because you simply stop jumping down shit and never miss it(my case). you don't have the time and energy anymore to skate everything, so you focus on stuff you find fun, approachable, and also achievable. and i think then it's totally possible to progress at that at any age or level. but the stuff you don't do anymore will inevitably get worse or maybe even disappear completely. and i guess for me and most people this happens around 20-25, because at that point you have to be somehow professionally involved with skateboarding to live that skatelife where you still skate everything and you skate all the time, but most people will accumulate responsibilities and be working towards a career outside of skateboarding. i feel like this is the age where skaters start to develop park and plaza habits heavily and maybe go less on street missions or even avoid them. also at that point people know what type of skating they like and double down on that instead of trying something new.
as a kid, you want to learn every trick, but as an adult, you only want to learn tricks you really like. you also don't approach skating from the point of how good you could possibly get, but from the opposite side. you already know how good you are and what you suck at and maybe don't care for, trying it out isn't as interesting. and at some point skating anything in flat and jumping around can be very painful, so old heads turn into slappy and transition skaters and then progress there. i think there's possibly no end to progress, but there's a point where you decide what skills you want to nourish and which ones you want to more or less neglect.