Well, it does seem to be a tricky question to answer, but try we must! Good answers so far, guys.
Just to look at one aspect, a physical one. It seems that, in general, as far as our corporeal state goes, here on Earth now, barring sickness or something of the sort, we are in our best form at 25 or so. What do you think?
I always felt 24 was still a bit young, and then 26, a bit getting on somewhere past an ideal number, 25 is the last beautiful number. It’s a perfect square, as well. Therefore, 25.
I was rather stupid at 25, spirit/soul wise but it was indeed a good age from a corporeal point of view. Older than that, I would prefer not,
This is not my final answer, however. Only musing.