My experience is that the sooner you experiment with your dog off the lead, the better. When they are very young, the world is a bewildering and scary place, and generally they will stay close to you and respond positively to you calling them.
If you go to puppy classes, one of the exercises they will do is to get all the dogs off lead, let them socialise, then tell all the owners to recall them. 90% of pups will respond immediately. You are their pack leader, and if you use a firm voice, they will do what they are told most of the time. The problems tend to come when dogs think they are of equal (or higher!) status to you.
I've never used food as an incentive to get them to recall, a firm voice, praise when they return, and lots of practice from an early age have always worked for me.
This is excellent advice (imho, of course). Although comes with it's stresses!
Our Springer Spaniel Poppy, now 5 years old, was off the lead when she was about 12-14 weeks old. Life was good, she loved running to us and doing everything we told her. Then she got a bit older, and a bit more confident and found an interest in birds she thought she would catch. So she'd run miles away to the other side of the field before (Eventually) giving up and coming back to us. She did grow out of that, and is, by and large, great off the lead now. But we know what drives her and when she's going to go mental - this is mostly with deer, squirrels, rabbits and sheep. So if we go anywhere, we make sure we're not going to see any deer/sheep before letting her off (squirrels and rabbits are small enough that they escape up a tree/into a burrow before she gets anywhere near them). Cows and horses she's fine with now - will give them a token bark if they're staring at her (she doesn't like being stared at!), but will largely just ignore them if we call or whistle her to stop being a bell.
From experience, if you have a dog with a high prey drive or is drawn to things that move - expose them to as much wildlife as possible as often as possible, from an early age, and they will slowly get used to it and then it becomes the norm and not something super interesting.
We didn't do this with Poppy (hence she likes to run rings around sheep - which she's only done once with an understanding farmer, fortunately! and attempt to chase deer (lord knows what would happen if she ever caught up with one - I wouldn't fancy her chances!) and regret it.
Half the battle with off-lead training being brave enough to do it. Long-lines are a good starting point, and if you can find an enclosed space where they won't get into any trouble if they do have a brain fart, that helps you with your stress levels immensely!