Our 7 month old dog is a little too playful

We have a 7 moth old Lab-Shepherd Cross. He is good every other part of the day, expect for walks and when he is tired.

For example, when he is over tired he usually tried to force people to play, and when they don't want to, he either nips at them, barks, or jumps onto them to get them to play. We've tried curbing this behaviour through positive reinforcement, but he isn't learning he shouldn't do that.

Likewise, he is too aggressive/excites on leash. He barks and pulls at all people and dogs he can see. We tried to fix this by distracting him with treats when walking by dogs and people, to keep him from barking. He figured out he can bark at them, and then try to look relaxed and distracted so we give him the treat, before he turns back to braking and lunging.

His walks have been bad enough that my mother bought a choke chain (which I have taken and hidden. I will not allow harm to come to the dog). What can I do to help my dog understand what to do when he is nervous and excited. How can I help him?

Edit: forgot to mention, we have a small 10 year old dog as well. He is 9 pounds. They don't get along well in the sense that the old one hates the puppy, and will bark at him and snarl for him to back away. Even when the puppy is walking past him, he will tense up and shuffle back a little. Anything I can help him with as well?