Playing with an "Old" Crone in the woods.
Have an old, wizened crone who's in her late 20s. Using her magic to save up her youth for times she actually needs it, instead of doing that old-fashioned "being around for a long time and gradually decaying". Getting your more infirm years out of the way first is a great way to enjoy your old age when you can really kick up your heels with the body that you skipped having in your teens. She has a lot more respect being an "old" woman in her trade, and a lot less guff from simple townfolk. Being old while still young also has managed to give her some important medical insights that she wouldn't have gained as quickly if she hadn't experienced them first hand. Everything else she learned from her book studies in her 30s, which hasn't happened yet.