i have 5 month old rottie when I take him out for walks he's really good....until we see people or other dogs his focus is on them starts pulling on the lead and he just wants to get over there just for attention and get stroked or if he sees people coming from behind again he will either purposely slow down till they get nearer so can try go over to them and sometimes afterwards he will start jumping up and biting the lead or biting my trousers or trainers its looks and sounds vicious but it's not just embarrassing. And I know it's good thing he loves people but not good when he's bigger and could scare people or accidentally knock people or child over just wondering if anyone had good advice for this ? Thank you

My young GR will do the grabbing the lead, trying to jump up thing when she is not allowed to do something. Usually it's because I've not allowed her to go and see any dog she pleases, or if we've walked past our car rather then getting in to it - she loves goes out in the car. As you say, it's not nasty or viscous, it's almost like she is throwing a tantrum because she can't get her own way.
Usually I know it's going to happen so I am prepared for it and a sharp 'ah, ah' before she gets going is enough to stop her. If she does start, I get her to sit (may take a while as your dog is younger then mine) and just stand quietly more or less ignoring her. When I think she has calmed down, I then go to move forward, if she starts again, it's back into the sit and we wait. She gets the message eventually, it's boring not going anywhere and she will stop being silly.

Yeah basically how my dog reacted if he don't get to see other dogs or get attention off other people walking past he will start jumping up biting my trousers or biting lead making load of noises and I do basically same get him to sit and wait and then give him treat then walk on again same process if he does it again.

Well you are doing the right thing and time will improve his behaviour.
When he does greet someone that he is allowed to, what do you make him do? I make my dog sit and encourage people to stroke while she continues sitting. Intially I had to keep making sure she remained sitting. Now she will spot someone she knows, run to them, then sit rather then try to jump up or make a fuss of them. With strangers she either ignores or approaches, but not with a great deal of interest these days.
Maturity helps, but keep up with your training.

Well I keep him on the lead when I walk him now cos when he sees people he just runs over to them and he won't jump up he will sit there but I want to stop him doing that cod when he's bigger that can be scary for people seeing a full grown rottie run at them. But when he's on the lead he will pull either back or forward to just get to them to get their attention and stroke usually he's happy after that but he goes def when I try to get him to focus back on me and he likes to run off with joggers and cyclists as well

> he likes to run off with joggers and cyclists as well

Then he has to be kept on lead and go back to training on a long line so that you have control over the recall.  It needs to be 100% recall before he's let off lead again. (Except in his own home of course.)