does this make sense? "il faut qu'on ait 16 ans pour boire du vin en France"?

This is correct.

One would be more likely to hear "il faut avoir 16 ans ..." (because the subjunctive is moribund in spoken French, and French speakers make comical detours to avoid it).

But you will be understood, and the grammar is beyond reproach.

...

D'apres moi les Belges francophones parlent un francais beaucoup plus pur que l'argot d'oeil qu'on trouve en france actuelle.

The second one, that starts "il faut avoir..." is better.

The thing with the French word "on" is that it can also be taken to mean "us" or referring to someone other than a single person.

Either could work, but the second is more correct. I'm guessing this is for a French class project of some sort? :)

Looking at one of the answerers above me, while they are Belgian, Belgian French is different from French, um, French. "Moins" means "months" and if you ever said " you must be 16 months old to drink wine in France", then even the Irish would be upset with you!

I would add "au moins" to make it even clearer, and write the number in full : ""Il faut avoir au moins seize ans pour être autorisé à boire du vin en France."