Why is marriage still such a rite of passage in our society?

I'm 24 and a lot of my mum's friends kids are around my age or younger and a lot of them are getting engaged. That's fine, it's nice that two people want to get married but what I object to is this kind of notion that it's expected. The amount of times I've been asked "will you and X be next then?" is slightly getting on my nerves. It's almost like a competition. It seems that marriage is still regarded by many as a mandatory rite of passage, and that until you've achieved it you're failing. Those that get engaged are treated like they've achieved some great feat, and I don't get it! I can understand in olden times when women got married to leave the family home but nowadays when women have their own lives and careers why is is still such an expected event? Marrying for love is fine, but why does that necessarily have to happen at any particular period in your life? What's wrong with marrying in your 30s,40s or 50s. Surely it all depends if you find the right person. Just wondering what your opinions of this are? Has anyone also had these slightly irritating comments from family/friends. Or does anyone not agree with me? Edit: I'm not really taking religious beliefs into account here. I can understand in that case.

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