I had been playing single player since release vanilla sup com around 14 years old. I started playing multiplayer at 18 or so, back when FAF was a few months old. I peaked around 2150 or so by 19. Hovered at low 2k off and on for several years of moderate inactivity. Then took 3 years off, back now at 27, with 2180 peaked ladder rating. While I do have an ungodly amount of hours invested in this game, I take solace in the fact that the 2.5k games or so are spread over nearly 10 years. But once you 'get good', its fairly easy to maintain a good skill base. I honestly think you can make top 30 on skill and experience alone, with a healthy dose of critical thinking skills. APM is only a limiting factor at the 2K+ ladder level, and even then we don't have a high enough pool of 'pro' players to really see it take over unless you are stuck laddering on the ditch.
I know of old players in their 40's or so who could easily come back and be a top 30 player. This game is great in the sense that you can go quite far with an APM of only 50-60 or so. I also know quite a few of the top 20 players started to explode in skill around 16-19 years old.
In regards to getting older, my reaction time and APM have taken a nose-dive as I have stacked on the birthday candles. Its mostly why I play FAF and Apex Legends instead of CSGO and StarCraft 2. You can rely more on fundamentals and solid gameplay a bit more then being really really fast.