I had my first at 25. I was the first in our group of friends to have a baby, it was not a planned pregnancy (but very much embraced).
Although now nearly all our friends have children, they are into their mid-thirties and I am looking forward to having a 20 year old DD when I am 45, when they will have 10 year olds! Maybe I can embarrass her and tag along with her when she goes clubbing?
Maybe not..! But my DD will be grown up and lots of my friends/colleagues will still be at the primary school gates in their 40s and some in their 50s!
I think that being a "younger" parent of an "older" child will also have its benefits - keeping active with them, keeping up with them, maybe even being a young grandparent and having more time to enjoy that side of life also. Also, still being involved in my career and hopefully, once the mortgage is paid off in the next 10yrs, having a nice bit of disposable income to spend on my lovely grown up children - hopefully by helping them through uni and other practicalities, but perhaps also nice things like girly shopping trips to NYC... we'll see what the future brings.
Looking back, I'm glad I had DD at 25. Sometimes I wish I was younger, then I'd have more time with her! There's a 4 year gap between my first and second DCs and even though I was 29 when I had DC2, I did feel much older! Years of experience perhaps!