I can't believe you all don't realize that being young or being old has nothing to do with how you feel, but everything to do with the actual age you are. There's a simple mathematical way of determining these things. Regardless of how young he looks or feels, a man becomes objectively old when he turns 40 (much like a woman becomes old, obviously, when she turns 27).
Incidentally, this means I am 26 years old in girl-years....
This is absurd. There really is no standard, it depends on the person. Yes, you could generalize that 0 to 30 is young, 30 to 60 is middle age, and 60 to 90 is old age, but again, really depends on the person.
A 60 year old that can bench press 350 pounds and run the mile in under 6 minutes and 3 miles in under 20 minutes is, you can argue, more fit than 90% of the high school and college age youth(14-23). Who is younger in terms of what they are actually able to do, this 60 year old or 90% of all youth?
As for females, they have yet to even hit their sexual peak at 27, so its absurd to be labling females at 27 "old".