Is there a minimum age a player has to be to play in the team? If so what is it? What's the scale of training speed to age ratio? Is it different in academy to coach training? At what age are they too old? What happens to them?
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25 is the max age and currently there's a plan for when that does happen, you'll be able to turn them into a coach. Nothing has been implemented for this yet though and to my knowledge any age can play in games right now.