Congratulations, MrEBear and Notsoold. The fabulous forties! However, I beat both of you out of the running completely, coming in at a stately and glorious 50 
!!! Time for a bit of a longer post here, to address some of the issues of having a child at an older than conventional age which, naturally, I've had cause to think about quite a lot.
To recap, I'm 8 weeks pregnant now, by means of an embryo transfer in the US, with my husband's sperm and a rigorously screened egg from our lovely 27-year old donor. My GP's initial response was that she thought I needed psychiatric commitment (!) and her mantra since has been "we've never had anyone pregnant at this age before"... The last time she said it, I thanked her with a laugh for reminding me yet again just what a total and utter freak I am! 
That stopped her.
When I joined MN a few weeks back, I expressed my worries about having a child at this age and had a lovely reply from a woman who had twin daughters by IVF, aged 50 in 1997. As she put it, contrary to everyone's expectations, she and her husband are still around and fine! Indeed, there's no guarantee that you'll be healthy or survive at any age. People continually get sick or die earlier; when cancer or car accidents strike, they don't pause first to ask how old you are.
So we'll be 65 when our son (we know it's a boy) is 15 -- the age of most people's grandparents. We're rather young-looking anyway and we'll trying to stay that way for a while. But hell, if he's embarrassed by us, that's normal; aren't all teenagers embarrassed by the parents for one reason or another? And, with dramatic improvements in IVF procedures, many more people are able to have children late in life. So we reckon that, in another 15 years, it'll be less unusual.
There's a well-worn criticism that it's irresponsible to have children so old and, indeed, we wouldn't necessarily have chosen to do things this way. We would have loved to have any of the 5 children we lost earlier to miscarriage. We could also have remained unhappily childless but the option not to came up. Certainly, it's a huge incentive to stay healthy, as parenting is for anyone; and we try to keep in mind that many people are brought up very successfully by their grandparents.
That said, we have also legally arranged for other specific relations to take over, if anything should happen to us. That's something many parents don't do but it seems wise, regardless of your age. We're lucky we have relatives who are more than willing and we've arranged for them to inherit everything we have, so it doesn't cost them. In other financial respects, we're also planning quite differently to how we would have otherwise. No silver-haired cruises into the sunset for us; more like investments in rentals, to provide income for a student with retired parents. That kind of thing.
Cliched though it is, you really are only as old as you let yourself feel and, while my husband and I are kidding ourselves about our age, we're also determined to remain distinctly immature and silly young in attitude. So try not to worry about it. Plan accordingly but also remember that the more worrying you do, the more you lessen your mortality!