My puppy is just over 5 months too and has been running free and at speed - his own speed, that is - since he had his final shots at 16 weeks. I worked with him in our (large) garden before then, teaching him recall. Which is to my way of thinking the most important discipline you can teach a pup. Oh and 'TRADE' when he has stolen something you cherish. He gets a bickie and you get whateveritis back.
I wouldn't force the running, but Mku picks when he wants to run, usually in ever widening circles if we are in the fields, or hither and thither along woodland paths, deviating sideways in pursuit of a squirrel. They do love to run - Mku's Mom is just short of her coursing title and Son-shine is showing a great deal of promise but no - I wouldn't course or race him until he is 18 months or so. However, free in the woods (now that they have reopened from total lockdown) he knows when he has had enough. Short sprints, sniffs, trotting along with Hoover, another sprint, doesn't harm him at all.
When you have them trained, the main thing is to restrict calling them back to only when it is absolutely necessary once the recall is pretty solid.
I have been worried that he wasn't getting enough socialisation during lock-down but have been 'socially distancing' with friends with dogs on public footpaths while the woods were a no-go area. Yesterday we met several other walkers with dogs, and Mku was absolutely fine with all of them. Tail almost uncurling as it wagged !
