At the very least, 30 minutes to an hour of fast-walking I'd say, or about 30-45 mins of off-leash play time should be sufficient.
Some goldens have faster metabolism than others, so be sure to balance it out with the amount of food. If he is too big, cut down on the food and increase the exercise. If he is too thin (unlikely), add a little bit more food until you can easily feel but not see his ribs.
By the way, welcome and I love his name - my first pet was a monkey named Poochi!