I know there are ways to in the other games. I've got level 3-4 characters and have just barely explored the first overworld outside Sorpigal.... and my characters are 21! I think is the ghosts doing it and I didn't notice until now. I notice there's no 18/21 or anything like that. Is there a way to cure unnatural aging in MM1. Thank you!

It's also worth noting that some of the high-level Cleric spells (i.e. spell level 7) will age the caster when cast. The manual does not mention this. It's not a problem once you know about it though, because by the time you have those high-level spells you also have the spell to reverse aging.