Every reputable airline will have a minimum experience level to be met prior to being considered for command. Hours, time on the line. A-lot of airlines overlay this with a seniority system which, in general, means that by the time your number comes up you have the minimum experience and often a great deal more. These seniority systems have therefore often prevented some very capable young operators gaining a command as early as they otherwise would of. With the advent of LOCO's all that is changing as in general they do not have a seniority system. So suddenly we are getting younger commanders. I'm not having a go at seniority systems, its just a fairly obvious observation.
The key here is minimum experience to be considered for command. You still have to pass a command selection and then training. That ought to look after the various variables mentioned here if the training department are doing their jobs properly. Unless, of course, you do not trust the training departments. Maybe in certain countries there is an issue but in the UK I feel the airlines get it right.
Surly the correct response is to applaud someones success whether they are 25 or 55 and to encourage those with the ability to push on and succeed. That success has been hard earned. Some of you sound like grumpy old men.
I do however totaly agree that we need to select and train the right people and if that is not happening in India or elsewhere it is a cause for great concern but it is not age that is the key factor.
As an aside you can train non tech skills effectively.