Likely opinion, though some Muslim states outlaw it till that age, or more often all together.
No, not legally. If the law states the legal drinking age is 21, then one has to be 21 in order to legally consume it, no matter who bought it or serves it.
In the state of Texas you can legally drink at 13 or older so long as you are in the eye sight of your parent, guardian, and/or spouse. And the parent/guardian/spouse must be at least 21. Also the parent/guardian/spouse must order the drink then give the drink to you. However the establishment has the right to refuse.