This is exactly the wrong thing for a 20yr old to do with 100k. (Assuming they have no other assets) When I was 20 I needed a reliable car (having an unreliable car subjected me to periodic unplanned multi thousand dollar shocks), buying books for school (individual stem textbooks cost a couple hundred bucks) Yes I should have started an investment account but given my other finances I should have been putting in modest amounts every month, but frankly when daily life is costing more than you make it doesn’t make sense to earn 8% while incurring debt that costs 15%. I’d say the trick is stability. The uncertainties of young life with no money cause things to cost more than they should.

If my children had a $100K windfall this is precisely what I would tell them to do assuming they had an emergency fund and no debt. If not, I would tell them to create an emergency fund, pay off reasonable debt, and then to invest the rest for 40 years.

Read and internalize https://www.bogleheads.org/wiki/Prioritizing_investments. It is simple. It is immensely useful.