They can do either. Age and a crap load of experience aren't really necessary elements for leadership. You're right, it can't be coming from your rookies, but you don't need to be 30+ with 1000 games in the league.
Also keeping Kreider basically means that you'll be sending Fast and Strome (maybe even Skjei?) out, unless they take the dumb and lazy route. Does that disposal of experience worry you?
Fast and Skjei would be the ones I move this TDL. Strome in a year or 2, for 'cap-reasons' and it's assuming he has larger demands.
Fast is a good performer, when used properly, leads by example but is not worth UFA money.
Skjei is an underperformer and does not lead.
Keeping Kreider and Strome for the foreseeable ( 1-2 years) future would be my plan.
Kreider performs and leads and is well worth $6ish M.
Strome performs and leads and is controllable.
IMO The 'lazy way' as you mentioned would be to just get rid of Kreider.
edit - further elaborated