Drinking/Smoking/Army age discrepancy

I was always amused by the fact that, in many places, the legal age for smoking is lower than that for drinking alcohol, and the age for joining the army is the lowest, or equal to the lowest of them. After all, smoking is probably more hazardous to one's health than alcohol, and an active military service may be even more dangerous.

However, it's pretty simple to explain if you consider just whom most of the laws are protecting. Turns out, it's not an individual, at least not directly, but the society as a whole. From driving laws and safety rules to public nudity, to separation of church and state, it's not about the individual who doesn't wear safety goggles, shows his ass in public or worships his god(s) at a public school, but about the society as a whole not willing to incur medical expenditures, be disgusted by a hairy ass or dive into a heated discussion about just which god(s) should be worshiped.

So if you look at it from this angle, it's quite clear that, even though smoking may be more harmful to an individual, it's hard to smoke enough cigarettes to affect one's ability to drive a car, while it's pretty easy to get drunk and hit other peoples' cars or other people themselves. As for the military service, army is essentially separated from the rest of the society, so whatever harm is done is done to some other society, benefiting (hopefully, at least) the society that sends it's army to inflict the said harm.