The vast vast vast majority of people do not die because their telomeres run out. So the most likely outcome is no change, standard person

However, if this person took care of their metabolic health, then they might live twice as long. The current human telomeres suggest a lifespan of 120 years. So this person with careful attention, might hit 240

Probably cancer, but if not they would age slower and look younger longer assuming they didn’t tan their skin to a crisp or something

Noticably? I imagine their skin imperfections would be twice as large… or maybe √2 as large?