I've never seen a bag yet that didn't recommend far more than a dog of that weight should eat.
At 7 months, you can feed twice a day.
How much?
It depends on several things:
-- on the present weight of your Lab and your best guess as to final adult weight.
-- the kcals per cup (the metabolizable energy per cup); this varies between about 225 for some foods to 450+ for others. It should say on the food bag (or give an 800 # you can call to get it).
-- the metabolism and amount of physical activity your Lab gets every day; more active dogs need more food, dogs with higher metabolisms can eat more food safely.
-- the age of your Lab: 2 month old pups need about twice the amount of food an adult dog of that same weight should eat. As they approach maturity, this declines to about the same amount as an adult Lab of the same weight should eat. E.g., my Puff weighed 6 lbs. at 9 weeks age. At that age she ate a total of less than 1 cup a day divided into 3 meals. Gradually her weight and appetite increased to the point she was eating 5 cups total a day (divided into 2 meals) at about 7-8 months age and 45-50 lbs. weight. At that point, she began skipping eating for a day or 2 and when she resumed it was about 4 cups total a day. Then she skipped eating again, and when resumed was eating less. Then skipped again and again with declines in consumption until, as an adult, she was down to a scant 2 cups/day total of 393 kcal/cup Kirkland C&R (similar to Diamond Naturals, not plain Diamond).
BUT Puff is one of those rare (10%) of Labs that self-regulate their food intake. Most Labs do not and for those you'll have to carefully observe your Lab's body condition and go by that rather than appetite.
You might start by feeding a measured amount 2X a day for 10 minutes and then pick up and measure the amount not eaten to determine the amount consumed. Then feed that amount for 10 minutes at the next meal.
But
do carefully observe your dog's body condition. It's better to err on the side of too little than too much. Several recent studies on Labs both here and in Europe have found that Labs live significantly longer and have significantly fewer health problems when fed about 25% less than normal throughout their lives.
If I can find the Body Condition System illustrated chart I'll ETA it.
Here it is:
http://www.purina.com/dogs/health/bodycondition.aspx