People are just different... I've met some 75 year olds who are sharp as a tack and some 20 year olds who are dumb as bricks. I've also met 20 year olds who would give Einstein and Stephen Hawking a run for their money... and some 75 year olds who struggle to remember a password.
I'm 43... There were people on my ground course ranging from the ages of 23-43... I scored the highest on the Ground Course exams. I have my Line Check (Twin Turboprop for a Regional Airline) next week and a lot of the training captains I've flown with over the last month have commented that age isn't really a big factor in their experience (I was curious as a lot of the new hires are in their mid-20's with <1000 hrs and was feeling a bit self-conscious as the "Granddad" of the group
).
So, I'd agree with Negan that it is more about your own ability than age.
Also, for what it's worth... if you can do simple addition/subtraction and multiply/divide by 2 or 3, chances are you can do the mental math required on a day to day basis
