Thanks for your query.Based on the facts that you have posted it appears that your fiancé has moustache very late at the age of 28.
This could be due low serum testosterone
or low pituitary hormones like LH
This can be confirmed only by getting his blood tests for estimation of these hormones.
Opinion of a qualified Endocrinologist
will be of much help to diagnose the cause of his getting moustache delayed.