Age is not as important as you might think, sure when I was pre twenties, I thought I would be done by 25, yet I am now almost 46 and still doing my thing on a skateboard, even with injuries and other things getting in the way over the 30+ years I have been on a skateboard, but what I find the most pleasure is not just how high I can ollie or what flip or other tricks I can still do or anything like that, but more just being able to roll around.
With that rolling around, enjoying it more and then being able to think about a couple of tricks here and there, which sometimes work, sometimes don't, but I have learned not to get frustrated and blow my top, get upset, lose it and then lose the interest in it, which I had often done when younger, as well as seeing some major meltdowns and mental breakdowns from beginners and pro skaters alike over the years, self included.
The biggest thing that I will always come back to from when I did lessons and ran skateboard events, especially for your situation, is that it is not about timeframe in reaching goals, but more in relaxing and getting your body to get more used to being on the board, which in turn will allow you to do more on it. In any group there was always the kid who could do whatever trick we taught him within a session or two, but then most took a lot longer, some took the whole term to learn, but we worked with them and they usually got there in the end. Some were always going to be better at it than others.
Trying the same thing over and over will not only make you more tense but will also teach your body to move in the wrong ways sometimes, and bad muscle memory is not a good thing - there are some tricks nowdays that I just do not want to land and I will almost do anything to get my feet from landing on the board rather than being comfortable landing and rolling away - 360 flips is a big one for me - but to take it back a step, if you keep practicing the trick and not doing it right, you are going to keep doing it like that a lot more often, than if you left it for a bit, just roll around and do other things, then come back to it every so often after trying other tricks.
This is why skateboarding is so completely different from anything else - there are no rules, there are no guidelines on timeframes, points of achievement, qualifications for reaching certain levels or anything else the way almost every other part of our lives can be measured, rated, outcomes achieved, etc. Every single person is different and I know while I was growing up, I was maybe the least skilled kid on our street, with some guys I skated with going pro and others well on their way there, but I stuck with it and enjoyed it for what it was - a fun thing to do. Never forget that.
I could quote so many amazing people right now, but really, this simple wooden toy has become more to us than we would have ever thought and we have been able to do more on it than anyone ever believed possible from back when this all started. Every day someone else pushes boundaries and does something more insane than the last guy (which we all see via social media or instant access), but it is not for us to compare ourselves to him or what he can do, more so for us to take note what others do, but for our own selves, just to do what we can do on it, on any given day and accept it for what it is.
Today things might not turn out as you planned
But there is always tomorrow, so you can try again