Were Dr Chrusher and Troi older mothers when their kids were born? (except for when Wesley was born) Were both ladies in their 50's or 60's?
Troi can be handwaved as being half Betazoid and maybe that extending her fertility. Crusher, we just have to assume that 24th century living also elongates fertility somehow. Unless the Ba'ku planet affected her.
Not even handwaved. Lwaxana, assuming she was about the age of Majel Barrett, was in her 60s when she was pregnant in "The Muse".