I would venture a guess that the peak years of an employee's productivity are between 28 and 38. Well, I think I'm using myself as an example for this statement. Anything much before that initial age denotes a time where an employee is still finding himself. Anything past the latter indicates a time when an employee should have had the chance to begin straightening out his priorities. By his forties, if all is on track, he should be attempting to have a more balanced existence. Remember, that peak decade doesn't really mean one's work is constructive or will necessarily lead to important results; it simply means one is willing to work too long and hard. Again, I guess I'm talking about myself.
My most basic belief still holds true though. If a person, irrespective of age, is defining himself though his work, he should have his head examined.