bring back youth casts, make each cast reduce age by 1/10 of that when using a
scroll, and make it cost 10k sps.

In addition to maybe a way to stop abuse of such a spell would be to cause the caster to obtain a tempory stat bane similar to that of doing the 1 task point temporary boon. Also I would make it so that the character receiving the youth must forfite X amount of experience.

Example
Taylon casts youth at Tony, taylon loses 10 wisdom for 12 hours, Tony on the other hand loses the 100k of non-spent experience he had just obtained.