In my case it's not immortality I am discussing. My characters are more like having a natural longer lifespan and youth than regular people like say.... Alexander Phoenix from AO. Its a mutation in p21 gene. The most you get is that 150 years of lifespan is normal and 200 years is rather... ok but to us who are regular aging peps.... that's a lot of years...
He ages much slower than you or I so even though his IC says he is 50 years old, his body functions like that of a 30 and he even looks 30.
And just imagine when he is 30 he looks like a regular young man out of the Army.
And he doesn't not exercise too regularly or have anything unusual with his lifestyle.
ScienceDaily: Deleting 'Anti-Aging' Gene From Yeast Greatly Lengthens Life Span