I don't believe it's an age thing at all. It's more of a maturity thing. For example, when I was 18 I was extremely mature, as was my husband (although we weren't married then!) We got engaged and I'd say we could have been emotionally ready then. However, we didn't want children then. We're now 26 (27 in a few weeks) and although I would have preferred to have had my first child earlier, I don't think there is any problem with my age now. I know people that are the same age as me that are so immature and just selfish really that they probably wouldn't be ready yet.
People are quick to judge with age, but I really don't think it should be about that at all. As long as you feel ready, that's all that matters, whatever age you are xx