Hi! It is NEVER too late. Lucky for me our Boxer went to training at 5 months. . . just behind your little one. I totally agree with the advice given above, but at the same time feel your pain. We have, what the trainer called a boxer with dominance complex; not good when he, at 6 months can pull me around. One of the main, and what I feel most important factors, is let him know you're boss - especially if you are a small frame female. Basically follow a few simple non-harmful, non-agressive tactics.
1) this is what i feel made the biggest difference for me. when there is undesired or dominant behavior, no matter where you are, flip him on his back, straddle him (but don't sit on him), grab each paw and secure to the ground, look him straight in the eye and firmly tell him "settle!" This puts you in the most dominant position and him in the most submissive. Eye contact is a key factor in this excercise. He will attempt to hang onto his last bit of dominance by staring you down. Wait for him to look away. After he has gone limp, let him up and praise him for a good settle. I felt like a complete dork when first doing this excercise, but Harley now listens to me more than my fiance.
2) when you're walking your boxer NEVER let him grab his own leash and pull/lead you around. stop walking, make him "drop" the leash and then resume walking. do not get into a tug of war with his leash. In my experience, even as a puppy, Harley always won the tug of war which makes him think he's the alfa dog of the two of us.
3) while he's still small enough for you to control, and while on a leash, make him sit, and stay. Then, firmly tell him to "come." If he doesn't respond, tug on his leash until he does and then praise with lots of hugs and "good come!"
I could go on and on with all the tricks our wonderful trainer taught us, but this should help for now. Good luck!