Bf Waiting Till Marriage

So it came up a couple days ago that my boyfriend wants to wait until marriage (we're both 16 turning 17 within the next two months), but the thing is that we'd discussed previously having sex when we were 18. I'm not upset that he wants to wait until marriage, however I am upset that he hadn't brought that up before, especially since we've been going out for around a year. Am I being rational or ridiculous? I'm so confused, and I'm actually a little hurt