Don't worry about ''waiting till 5 months'' - I did exactly the same thing.
I know ''the earlier the better''/''first walk'' etc etc but actually, in the teenage months puppies will want to wander off regardless of whether or not you let them off first walk...or not! There's plenty of ''recall failed'' stories here on COL. I used a longline for a couple of months and slowly let the distance between us increase.
My own puppy who is almost 9 months had 1 episode of running away from me when he was given a new Kong toy on a walk (he was around 7 1/2 mo), but that was because it was brand new off the shelf and he didn't want me to have it. Now I hold on to anything bigger than a ball, it's MY toy and he gets to play with it, not the other way around
Another time he may ignore me - but not run off as he did with Konggate - is when there's mud or a person he likes the look of. I have to be one step ahead of him, as everyone does with a ''teenage puppy'' and hold onto his harness until I know his interest has vanished and I let go for him to run about again.
We're in the process of teaching recall to whistle and I really recommend it, blow the whilst when the puppy is already coming back. If he's having a lazy day, I also take a squeaky toy with me, drop to the ground or RUN AWAY shouting his name in a silly voice/waving my arms. All dogs no matter what age or breed love ''chase'' - if you run after them/''chase'' them they'll run away, if you run away from them they'll chase you.
Basically just have things in place (like toys, treats or a longline if you're in a ''fun'' place like woods or large park) to ensure the puppy never decides to make its own fun - you're the provider of all things fun. They will test you on any subject - not just recall - during the teenage phase, like any adolescent
It's always going to be nerve wracking, it is for me....they are so special and we wouldn't want harm to come to them.
That's why I waited so long....