Celeborn's age

[Landroval]

I wouldn't say the remarriage of Finwe was unique - though it may have been the only recorded one:

Originally Posted by Of the severance of marriage, Later Quenta Silmarillion, HoME X

Thus it is that the cases in which remarriage of the Eldar can take place are rare, but rarer still are those who do this, even when it is permissible. For the sorrow and strife in the house of Finwe is graven in the memory of the Eldar.