Question

in forties和in his forties的区别

Answer 1

意思是“在（某人）四十岁左右”
in forties和in his forties在用作后置定语时或做表语时，没什么区别。
in his forties，可以置于句，作状语，而in forties一般不这么用。
个人理解，仅供参考。