Thanks for posting your query.
Sunburns are more common in fair skinned persons.
He is supposed to use sunscreen on all exposed parts. The Sun Protection Factor SPF should be above 15 usually.
He can use SPF-30, since he is more prone for sun burns.
He is supposed to use it even if he is at home.
It would not be related to puberty
, hormones or thyroids.
Hope I have answered your query.
Wishing you good health.