It's a decent food and much better than purina, so you should be ok feeding it. There are better foods out there, but i don't know what your budget is and what's available in your area.
That 1.2% is the minimum calcium percent, not max. When judging calcium in food and if it's ok for a large breed puppy, you need to always go by the max amount. If you can't find that maximum amount on the bag or website, i suggest you call the company who manufactures the food.
As for it being an adult formula, it's not big deal. A lot of people here never feed large breed formulas, myself included. Just make sure the ingredients are good and the MAX calcium percentage isn't about 1.7 or 1.8 and you should be fine.