29 years. i wouldn't have chosen that intentionally, because it did make things much harder at times, but with the exception of being out in public, it was largely a non-issue.
a lot of my friends were like "how could you ever have that much in common with someone so much older" but similar interests are similar interests, i guess. we had a lot of fun together.
it didn't work out in the end, but those reasons weren't particularly age-related.
it does seem kind of weird to me now in retrospect, but at the time it didn't. we met over the internet (of course, right?) where age is so much harder to pin down and so much less relevant, and were good friends for a couple years before we met in person and it became a romantic relationship.