Cant build wonders with later era starts

[MasterMishi]

e.g. cant build Great Library in a medievil teamer or the henge, can build great wall. why?

 

[Smote]

Its working as intended, I believe. The probable reasons are balance and the fact that people shouldn't be making ancient wonders in the medieval age. It has the wrong feel for someone to make a modern "Great Lighthouse" for example.