If someone looks 13 years younger than their age does it mean they have good genes?

Partly. I think lifestyle comes into it as well. When I used to go to my annual workplace health fair regularly, I would always have a metabolic age 15 years below my biological age, which pleased me no end as a bloke in late middle age. They've changed it now and reduced the number of tests so it's apparently not as good and I no longer bother. My lifestyle is pretty much the same and my diet is healthier than it used to be so I'm guessing I'd probably still be okay (apologies for the humble bragging 🙄).

Definitely. I've been told I look much younger than my age

Yes, genes mostly the biggest factor.

It means they have Lulujeans😃