My mum had me when she was 20 (I was an accident but she and dad were already engaged
).
I only had ds when I was 39 - but there again, I only met dh when I was 32, got together when I was 33 and we got married when I was 37. Took the decision to ttc within a year and then took less than a year to conceive.
My mum was a wonderful grandmother - but unfortunately, she had a cycle accident at 66 and eventually died from the consequences of her injuries at 71.
Shit happens 
My dad however is still going strong at 81 and I fully expect to have him around for another 10-20 years (going by his family history
) as should mum if it hadn't been for her accident
At 57, I'm fit and healthy - as is dh (59). If anything, ds keeps us young - but I think we'd have been running, cycling, rugby refereeing, exercise DVDing, Pilates-ing, anyway
. I'm even considering starting playing rugby!
(Or at least, going along to the Ladies' pre-season training
Ds will be mortified but he's off to Uni in September so he's not going to be around anyway
)
It's not selfish to delay it - you will still be a good mum/parents whatever age you have your kids
. Indeed it's arguable that it's better and less selfish to be in a good/the right place emotional and financially. But the downside is a potential personal one as you have less time to investigate if there are problems - and especially if you want siblings (speaking from experience and two MMCs
).