In practice, depends on where you go.

Socially, pretty much every 16 year old kid has drank some alcohol and usually if its with your parents you'll be fine. What's frowned upon isn't really drinking, it's getting drunk.

Here are the two situations that may come up, If you're in a bar or buying in a supermarket , they will ask for your ID if you're the one buying, almost always. As for restaurants, some are very careful on serving minors, so they might ask for your ID, but if you are with your parents and/or they are the ones ordering it for you, you'll be fine.

Another thing you need to be careful with is public drinking/smoking, police are very careful with minors drinking in public places , but as long as you're in a house party , or drinking with your parents indoors, you're fine.

Smoking is slightly different, the laws are very rarely applied, most of the time you're fine. I've seen 14 year old kids not only buy cigarettes , but also smoke them in public without fear.

Here's a rule a thumb, don't smoke or drink in public , or at least , not in front of the police and you're fine 99% of time , expecially if you're with your parents. France is very chill compared to other places I've lived.