Need expert ppinion on getting a vasectomy at age 21?

Not recommended: As you may decide you want children later in life, and vasectomy is not always reversible. Contraception is relatively cheap and easy to do. Don't make a rash decision that you regret later in life.

Okay..., but...: Vasectomy can be done on any man after proper counseling for its indication, procedure detail, possible complications and realistic expectation as a permanent procedure although it is potentially reversible. After thinking those over for 1-2 months with no change in personal decision, proceed with vasectomy under informed consent. That is nothing unusual in practice. Best wish ... Always.