Yeah it is true. I think the ones that all quote 30 will probabaly find it slipping to 31/32.
I am in Hampshire but not that far from Surrey so maybe theirs a geographical thing, but I am not convinced.
I think maybe its an aspirational divide. A bit like there used to be a class divide. I don't think its so much class but an apsirational/lifestyle divide. Those women who want a good education, a good career, an expensive wedding with "the one", a nice house full of nice things, decent car etc all before having children delay having families. I just don't think there's time to do all in your 20's and certainly when you have all those things it costs a lot of money to keep those things so you can't afford to maintain your lifestyle and have kids. Whereas if your priorities are not education/careers/having lots of nice stuff then I think having children becomes more plausible.
I suppose it really comes down to not being able to have it all; there is no way you can have kids in your early 20's (unless your husband is older and richer)and have the education, career, big white wedding, and buy the house to fill full of nice stuff as well as a fmaily. So people have to choose. My mates all seem to be following the traditional uni, career, marriage, buy house, fill it full of nice things route and in RL I don't know anyone who has chosen the other route, but MN proves there are plenty of people who do.