In a lot of lores spellcasters can live several hundred years but they often age at the same rate as mortals.
I am glad they're not the exact same as vampires. Vampires are gifted with Eternal youth at the cost of being a parasite that must feed off a host's blood, as well as an aversion to sunlight .
It makes sense that a witch would constantly need to reapply a potion to stay young forever.
That being said, I wish the potion of Rejuvenation turned anybody that drank it into a young adult. So if an elder drinks it they become young again.