By mn and this threads standards I was a fairly "young" mum at 28, almost 29 BUT we'd started ttc/stay pregnant from I was 24. I have endo and had multiple issues that meant dd didn't come along until then, people who THOUGHT they knew me well commented they were surprised I'd waited so long (I was always "baby daft" and a nanny before I was a mum plus loads of babysitting etc), but these people didn't know about the mc, surgery, medical treatment etc I'd had to deal with before dd came along.
As I'm now divorced and ex has turned out to be a shit dad I've had criticism on here and in real life, but I'd been with him nearly 5 years before we married, there was no indication whatsoever he would turn out to be a lying, cheating, deadbeat piece of shit! He was incredibly supportive of my medical issues and very keen to be a dad, his own family and close friends he's had since primary/early high school age were completely shocked (I swear it hit a few harder than it hit me!!) at his behaviour. Prior to us splitting he was critical of deadbeat dads and even fell out with one friend for fiddling child maintenance. Sometimes you get completely blindsided!
My friends vary greatly in when they first became mothers, from teens to 40's, but to be honest not one of those I'm close enough to know was it really "career" or "money" (which is not to say these are perfectly valid reasons just my experience) it was primarily 1 of 2 reasons
1 not meeting/being with the right person (couple of abusive twats, thankfully my friends are now away from them, few idiots who did that crappy thing of postponing indefinitely then sodding off with a younger woman and almost immediately having children with them having basically wasted most of my friends' fertile years, gay couples who were wary of how hard/expensive it would prove for them to achieve parenthood...)
2 They have actually been wanting/ttc for several years but various health issues have made it difficult. Multiple mc, fertility issues, ill health (inc cancer) but they're understandably not necessarily making this public knowledge if they can avoid doing so.
One friend has had a lot of shitty criticism for having a large gap between her 2 from people who don't know her well enough (and therefore should keep their traps shut!) to know that her and her husband were ttc from when eldest was just 1 but they had problems with secondary fertility and then several mc. They'd actually have loved a closer age gap but it didn't happen for them.
I've had crappy comments in the past about having an "only child" from people who don't know that due to medical reasons I couldn't risk another pregnancy.
Fact is you don't know people's reasons and nobody should judge a persons choices on such a deeply personal matter.
There seems to be a perception that fertility issues, mc etc only affect older mums when it really isn't the case. It's more that women with fertility/gynae issues as a result of this don't become mothers till later.
There are huge problems with gp's and even gynae's fobbing women with gynae issues off for DECADES. So not only are the problems not DX or treated they worsen in that time, which can include reducing fertility, they're not being treated.
It took 14 YEARS until I was DX and that was the ave for endo at that time, it's currently around 7-8 YEARS. Sufferers of other conditions will be more aware of the stats on those but I believe (happy to be corrected) that pcos is around the same. I'm afraid I don't know for other issues.