She was raised to Ajah Head after only 72 years with the Shawl (which would make her about the same age a several of the "too young sitters" when she got this role. Given what we've seen of the other AHs I suspect most are much older (like 200 years with the Shawl). Much like Sheriam who made a rapid assent at a very young age (even more rapid than Galina).

20 years back, before Siuan as Amyrlin, Leane as Keeper and Sheriam as MoN ... not to mention the rash of too young Sitters brought on by the Tower Split ... Galina would have been an anomaly as AH.

As I said in my earlier post I also believe she was likely already on the SC at that point as she would have needed at least some time on the SC to work her way up to #2 ... thus she was young when she first made her way onto it. I suspect the SC wanted a member of their group to become AH after the "troubles" to make sure SC directives were directly effecting the Ajahs ... The Red was most likely simply the first opportunity for them to place someone.

I'm not saying that Galina is necessarily very young at this moment ... although I think even now if she was raised AH she would be considered very young for the role, as you note she's a good 10 years too young to normally be considered for the Hall. But I am saying she rose rapidly at a very young age within the BA structure and through that the AS structure. Much the same as Sheriam.