and ride it for 15-30 years.

If he wants to be a landlord, he can always rent out and cash flow--the ridiculously low mortgage rates we have now should be very appealing later on down the road. Or he could start a small business / partnership.

If he's trying to invest in something short term and get anything more than 5-6% interest, it should be "fun" money, and he should be willing to lose all of it or a good portion of it.

Otherwise, he should invest in his 401(k), HSA, Roth / Traditional IRA, and/or 529s. Those all have some tax advantages and should be maxed out before seriously investing in taxable accounts.