If there is one specialism where age should be firmly ignored it is spin bowling IMO, especially finger spin bowling. Of course fast bowlers benefit from experience but unless they're Courteney Walsh the experience is usually more than countered by loss of pace, injuries etc.Probably Gary Keedy of Lancs (SLA), but he's a bit of a bunny so is unlikely to ever find favour with Big Dunc. Same deal with Jason Brown at Northants (off spin), although Brown hasn't had a great year so far. Both must be into their 30s too, so hardly the future
Not to mention that most spin bowlers have finally managed to learn how to hold a bat by their mid-late thirties
And unless they're something VERY special, the test arena is quite possible not the best place to gain that experience.