If the problem is magical healing, why not reduce magical healing instead of shortening someone's life by 1% every time they're healed?
Cuz, to be honest, the aging thing seems like it would be a great incentive for someone to only adventure for, at most, a few weeks before retiring. If I know that by being an adventurer for the next two years means I am taking 20 years off my life even if I live, I am not likely to try it.
In most source materials, the reason that adventuring careers are longer and more spaced out has nothing to do with aging or even with the availability of healing magic: it's travel time, from place to place.
I think the rules you are trying to implement are counter to your goals (e.g., by making shorter adventuring careers even more attractive), so you might want to reconsider the rules, and go back to whatever you think the big problem is.
If the big problem is magic healing, then address that instead of trying to force the aging system to do that.
(That said, since we're not talking about 5e now, but for some reason about your own game system instead, this probably isn't the place for this conversation, is it?)