I'm not sure that can be considered evidence, but wouldn't Shojo being able to move while wearing plate armor indicates that he has more than the 4 STR estimate given to him due to his age?

I mean, regular full plate is 50lbs, and nothing implies his armor is made to be lighter via magic or special material. It is also unlikely that it is not full plate.

Furthermore, Shojo has shown he was able to casually lift approximately half an humanoid skeleton, which isn't that light.

I'm not quite sure of how to estimate his STR based on that, though.