The oldest verified mother to conceive naturally (listed currently as of 26 January 2017 in the Guinness Records[44]) is Dawn Brooke (Guernsey); she conceived a son at the age of 59 in 1997.[45]
I mean it's possible but feels weird because of the setting. It's seems to be around feudal japan which means people have children at younger age because of technology and expectation. On top of being women of some standing which expected to have children at younger age to ensure lineage.
Though I think it's more of the mangaka trying to make her beautiful middle age woman just by adding few lines under her eyes