I know the feeling. DH and I have similar features and dark hair. His sister is blond. So is my DD. Anytime we go anywhere in public people assume that she is his wife and I am his sister.
Anyway, there is a local mexican restaurant that we go to often, usually with the kids. A few weeks ago DH and I were in their by ourselves. First off, we NEVER get carded in there. Second, everyone knows we're together because we're often in their with our kids. Our server cards us, stares at the IDs for a LONG time (I'm 28, he's 33, the math is not that hard). Then the entire evening keeps asking us if we're on the same check!!