Just an idea, I personally don't care if it gets used or not...
If we're going to make ages come into play with things around here, I think the best way to go about it would be to have people automatically start with an age between 15 and 25 and then if we use Neil's sim, as they age their mental strength attributes could improve over time.
We could then have it set so that there is indeed a retirement age, although at 65 it would take someone a good 50 seasons of Dev League cricket to get to there.
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Strength and speed would naturally decrease after a certain age, though, I would imagine (35? 45? 50? I'm not really sure). I think this would enhance the whole 'career' aspect of this league as well as realism.
Of course, there are probably more important things to think about, but if Neil's sim does indeed come into play in future seasons then it would be great to allow players to "mature" from youth and then at some point begin natural degeneration. It only makes sense to have the average 15 year old to increase in strength and intelligence as he reaches the age of 30 or so, and for his agility to decrease from that point on, and then eventually strength decreasing as well. It might also be reasonable to say that fast bowlers would become fast-medium bowlers if their running speed decreased at a certain age to beyond what would be required for a fast bowler.
The reason I'd have people starting at a young age regardless of their offline age would be to allow older people who might happen to sign up to be given the full distance.
It would also add to the realism of a bunch of youths making up the first ever CW XI and then over time, the youths mature into seasoned players (those who would be 15-20 in the first season would be 25-30 by now).
EDIT: I say "15-20" because I think people should be able to trade off the U-19 option in favour of a stronger mentality & physical strength.