It's also worth bearing in mind that having children seems to have taken a toll on Elven women - this is/was being discussed in another thread
Luthien and Galadriel - and so it could well have been that Celebrian went through a fair amount of struggle in bearing twins!
What interests me is that if it was a custom to marry at a young age, would characters such as Arwen have been seen as 'on the shelf'
as it's so delightfully put these days? There seem to be a fair few characters who this would apply to, including Legolas, so was it a case of the higher status Elves having to wait longer until a partner who was 'approved of' was found?