No to the Certificate of Depreciation (CD) for sure! It's basically a savings account where you have to leave your money parked, and you might get a certificate to tell you it's parked there. You already know what an impressive return you get from a savings account.
20k on hand at your age is awesome. Put as much into a Roth IRA as the law allows and let it build compound interest so you can retire a multimillionaire. Don't invest in individual stocks - there are plenty of mutual funds that will average 10%+ annually over the long term. You won't do that with individual stocks unless you happen to get lucky.