At his age stock market all in
The potential gains are greater, but so is the risk. Our young friend seems very risk-averse. I would suggest he become very familiar with the Stock Market, before risking his money there. Or he could entrust his money to an investment company. Of course you have to trust that they are legitimate (do your due diligence), and even if they are, they'll tell you 'Past performance is no guarantee of future earnings'. So the potential to earn more is there, but the risk is higher.
A CD or money market account from a Bank or Credit Union is very low risk, and are Federally insured up to 250K.