I can't think of many 65 year old pilots who don't drink more than they should, don't have a pot belly, don't eat too much curry, etc...
Leaving it to, say, management to decide who gets the chop after 65 and who doesn't (based on performance) is going to be a horrible task. "Come on everybody, we're having a retirement party this week for the most recent pilot culled for no longer being able to fulfil his duties"! Therefore, leave the arbitrary retirement age as it is, is the best option for everyone. Even those who don't realise it, Wayne.
I'm only guessing, but those that need to work beyond 65 (or even 55, realistically) are probably those who played away on a night stop, knocked up some poor cabin crew lassie with questionable taste, and are now paying for an expensive divorce. The younger generation should not be paying for your foolishness!