I've just trained my family's 3 year old lab to walk on a loose lead. I clicker train and have tried a few methods because no one else is willing to train the poor gal and she's put out the backs of the two people who walk her on several occasions (myself included and I'm only in my twenties!). I've also gone through countless expensive collars/halters and after two years of consistent training and trying to do what we're taught at obedience class, she'd only walk properly in the back yard.
I succeeded entirely by accident. I had Brodie walk in a small square and then each time she did it, expanded the space to another square. So we started with one concrete slab at the verandah and then just walked in squares and then rectangles, increasing the space every time she complied. After that, I expanded the space to include the driveway and the footpath in front of the house. I lost my clicker at the time so I just made sure to use praise and small treats (first regularly and then intermittently) and call out to her, exaggerating my footsteps really slowly and loudly before turning corners. I also chanted 'SLOWWWWWWWLY', in case she didn't get it ;). I changed direction and pace, zig zagged and was spontaneous in my actions to mix up the routine and encourage her focus on me.
After about 4-5 sessions before breakfast, she's now able to go for a walk without us having to pace the verandah and driveway first. This is an independent dog that refused to listen to anyone once she left the property and chased everything with her nose . I don't know why it worked after everything else (I had tried incrementally increasing space as a reward at other places). Maybe it was mentally tasking for her. But whatever you do, it's really a matter of trial, error and a bit of creativity.
Best of luck, you're lucky you have a pup and the opportunity to avoid a few trips to the doctor, courtesy of an (im)mature adult dog! Loose lead walking is not an easy thing for some owners/dogs.
