The question I have is are they are going to recast River with someone younger? Alex Kingston is 47 or so, and I think it would be really hard for her to play a younger age believably. If River led a long life of adventures with the Doctor she had to have met him when she was what in her 20s or possibly early 30s.
Presuming that River ages at the normal current day human rate.
Presuming that River ages at the normal current day human rate.