doesn’t have to sell it right when he returns and by then it will be long term capital gains. Index funds would be safest for investing in the market.
Cd’s would guarantee 4 or 5 % but who wants that? That’s only like $1k more than today’s money.
If it wasn’t a surprise I’d say open up 2 accounts and put half in a roth and half in a non-retirement that he can access sooner.