Thaaaanks. :D Well... How old is old?! Maybe this is up for debate.

I come from a sports/military piloting background, where somewhere between 18 and 25 it's the peak and after 30 you should start thinking about your retirement.

Of course this doesn't mean people over 25 are "old" literally, but in a learning context I think so. I've learnt many things between 20 and 30, like french or dancing, I still play tennis and it was common to see people 10y younger progress much faster then people my age. It's natural to have other priorities and worries to steal focus away, thus making it harder/slower.