When I was younger I trained with our local badminton club for 2 and a half years the I stopped for 7 years until today. I got most of the skills from that training history and I still manage to play fairly well ever since. However I want to start formally training again now that I have more time in my hands. Will it still benefit me at my age or will it be harder to level up?
I heard an interesting bit of commentary, I think it was during the SSF. They were talking about how older professional players (28+) were sometimes outcompeted by fellow countrymen like Axelsen. They said it's all up to the mindset of the player, whether you think you can do it or not At age 21, you can definitely still benefit!
Of course it depends what your goals are. Do you want to train simply to get better and compete in local tournaments? Or are you aiming to try to compete nationally and beyond? Either way, since you aren't starting from scratch, of course it's not too late to start training again.
Just think, Boe is like mid 30s. And would you really wanna play against Ramussen or Peter Gade? You still have plenty of opportunity to be a great player.