In the UK the average marriage age is 31 for men and 29 for women, granted tho quite a few will have kids before then but even when they don’t u don’t see many women around that age struggling to concieve. Most desi inlaws/parents are desperate to have grandkids for social reasons (how sad is it when some mothers actually act as tho it’s a race to see who can become a grandmother first 
) , in health terms it’s not exactly that much of an advantage to have kids in late teens/early twenties..
I saw this programme on some Bangladeshi channel the other day about a remote island where all the girls are married off not long after puberty. One girl was actually saying that she was considered **too old for marriage at the age of 12. **A lot of them ended up as grandparents in their thirties..Wasn’t unusual for their husbands to get younger models as well as they got older 