I've said before on similar threads and in general I stand by it. If a man is interested in marrying, making a relationship permanent and properly committed then they usually do so by around 3 years max.
Occasionally it's longer with particular personal reasons at play, but yea generally speaking if they're not proposing or at least initiating the discussion in that time period then...they're not that into you
That his friends who likely know him well? Think he's unlikely to marry any time soon if at all then they're probably right
Time for a brutally honest conversation
Like you I had potential fertility issues to consider and when I met my ex I was very clear I too wanted 1st child by 30 at latest. I didn't have a dx at that point but I'd already had one mc and I knew there was something wrong due to how my periods were and other symptoms from the start of menstruation. I later got a dx of endo.
You don't have time to mess about/be strung along and being married before dc is usually best for most women, especially if personal and financial circumstances mean your likely to go part time or be a sahm.
He's not so young that it makes sense to be commitment shy indeed he's at an age when most functional adults do settle down or start to think about it at least.
Ex and I were much younger but it didn't seem to us at the time as our friends and relatives were or had all married/had dc around the same age or even younger.
We're also of an older generation where couples did marry and have dc a bit younger I'm 49 he's early 50's so probably closer in age to your parents
But that also means we have life experience you don't as yet.
As I said, ime if no definite plans around the 3 year mark they're usually not interested. Yes I've known couples get married and have dc way after that point but I've not known it work out long term when that's the case.
Arguably ex and I didn't work out either but I don't think that was due to getting married 3 years ish into relationship. I think we were just too young generally (I was 22 when I married)
The couples I know who married over age 25 approx 3 years into the relationship are still together 20/30+ years later.
The reason I think is because they were on the same page from the start.