Why some people can deal with the cold

A question formed while reading this article. I was going to email a college professor, but I think there are probably folks on HN who know the answer, and my guess is that other people have a similar question. The article is about a mutation linked to cold weather climates and should take readers with an average level of English proficiency <13 minutes.

The study cited in the article uses data from “healthy young males 18-40 years old.” Are there studies trying to discover whether mutations have to occur by a certain age and in the absence of specific environmental conditions those mutations won’t initiate?

An example loosely based on the article would be to imagine someone lacking α-actinin-3 was born and grew up in Miami. Raised by her single mom, they rarely had extra money to travel. Occasionally they would visit family in Jamaica. After attending a local community college she earns a scholarship to Berkelee College of Music or MIT. She’s now 20 years old and has only spent time in warm climates before experiencing winter in Boston. Will the mutation fail to express itself?

If you don't know the answer, but know where to look or someone who might, please direct us.