Do you remember your reaction when you first learned “mężczyzna” is grammatically female? I know, I know it sounds so strange. Even worse when you need to change the endings like it was a woman but the adjectives stay masculine. Let’s revise it!
You should say: To jest dobry mężczyzna. not: To jest
The same rule will apply to all the cases and other masculine words ended in -a. Can you remember any?
Time for an exercise!