I have really poor night vision only in my left eye due to cataract?

Possibly. You are a little young to have a cataract, but it is possible. However, there are numerous other reasons for decreased vision at night. You should see your eye md for a complete examination.
Probably. But one needs to rule out some diseases like venous stasis, glaucoma etc. Hey! i got a great idea! why not see an ophthalmologist!