I don't have advice, but I have ballpark statistics from my home country, Canada, to reassure him that growing up is a more gradual process than he might realize. An estimated 42% of Canadian 20-somethings lived in their parental home last year.

http://www12.statcan.gc.ca/census-recensement/2011/as-sa/98-312-x/98-312-x2011003_3-eng.cfm

What is to give light must endure burning.