He's a pretty boy. He's just growing up and going through an awkward phase. Keep taking him out, keep socializing him. Do lots of training, so it builds the bond between you and he, and he will understand that you got things covered. He needs to mature. He needs to gage his reaction to your reaction, so if you are not confident he will be likely to over-react.
Wheels are tough for some dogs. They don't move natural like legs do, they make a sqeeeeee, the whirrrr, and they move like running almost. Some dogs will react to people on skateboards, bicycles, roller skates and strollers. If you have a bike path in your vicinity, it might be a good idea to go to the path regularly. At first on your walks, get totally off the path when you hear wheels approaching. Use your obedience and tell him to SIT. Correct for inappropriate behavior and move on. Praise any non-reaction and move on. As he becomes more familiar with them, he should settle down considerably.
Where did you get your boy, you can PM me if you want.
RIP Arwen, CD RN CGC
RIP Whitney, RN CGC
Jenna, RN CGC & Babs, CD RA CGC HIC (not AKC)
Heidi, RA CGC & Tori, RN CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear