I didn't plan on marrying before I was 30. I had no plans about marriage at all back then. But I did get married before 30, way before 30. I am long since divorced from my first wife.
I didn't realize until way too late that I married her for all the wrong reasons... emotional baggage and all that. If I was doing it again, I would wait until at least closer to 30.
That being said, I don't think the number is as relevant as a person's emotional maturity, expectations, and so on. It's great to wait until you are older and wiser, but it's also nice to share more years with the person you love.