I've never had a problem, and I look rather young. Just looked at the picture, looked at me, looked at the picture, looked back at me, and said "have a great time, here's your wrist band."
Just remember, if they DO give you a problem, they are only doing their jobs. If they make a mistake and let an under 21 person in with an "okay to drink" wrist band and get caught by the cops, the CM not only gets fined, Disney gets fined, and the CM gets fired. They'd rather make the odd guest unhappy than risk thousands in fines and an unemployed CM.
Go with an i.d., and if you don't look like your photo, bring some back up or get a new i.d. with an updated picture. Have fun!!!