Some people are just odd about 30. I looked forward to 30 from the time I turned 17 (thereby ruining my extremely dramatic and stupid feeling that I would die tragically and unavoidably at 16). (alas, I turned 30 and then my beloved mother died...so that sucked)
As all of my friends turned 30 and beyond, I was preparing for my wedding...and one friend chose to share the following with me..."I'm so glad I had my child when I was still in my 20s, later is just too old". Aw, thanks so much, lady!

Hey, friend, why don't you and your tiny waist try on my wedding gown, in front of me! Oh, and look up how much our photographer is charging us. And criticize us for it. Those are great ideas! (two things she actually did)
I'm liking 40, which is very different from my friends...then again, I did get carded the other day (not one of the "we card everyone" moments, either), so maybe there's a reason I'm enjoying it.
Anyway, some people just have a hard time with it...I've been thinking about age and relativity of age since I was a teen, so none of it has really been a surprise, or scary to me except from FAR, off.
Oh, also, I felt far older at 27 than I did at 30, and I feel younger now at 40 than I did 10 years ago...so perhaps they are worried that they'll feel older and older, even though it might not be the case.