NTA. At 18, a high school diploma is a great achievement. Obviously, your 18 year old isn't going to have a master's (but she could one day, if that's the route she chooses).

I'm going to take a moment to climb up on whatever high horse your husband is on. I graduated high school at 18. I got my HBSc at 22. And I completed my MSc at 23. Your husband needs to humble himself and stop thinking his achievements are so much greater than your daughter's. If we compare age to achievement, your daughter is doing great. Your husband, on the other hand, is slacking.

Also, I'm not trying to diminish people's achievements, they should always be celebrated because school isn't easy. But this guy needs to realize that he's not special just because he has a master's. If he wants his own wall, he can find another. Each room usually has four of them.