in my 21 years

Could you conclude from the phrase below, other than the author being 21, eg he’s been a Spurs fan for 21 years (the topic discussed was whether today’s squad is the best ever)?
Thank you.

“I can’t see us winning the title, pessimism comes naturally to us Spurs fans. Best side I’ve seen in my 21 years by far though!”

You can conclude that this is the best side he has seen in 21 years of something, but what that something is, we are not told.

It could be 21 years of living (so he is now 21 years old), but given that he wouldn’t have followed football for the first few years of his life it is more likely to be 21 years of following this team.
Depending on the wider context, unquoted, and possibly unwritten, it could also mean 21 years of living in that country, 21 years of doing that job, etc.