I have never fully trusted grownups who don’t drink coffee.

Drinking coffee is one of the key privileges of reaching adulthood. Failure to avail one’s self of that privilege is suspicious.

Adulthood, in regard to this argument, covers a fairly wide range. Any young person who is not curious enough to try a cup of coffee before the age of about 15 probably is doomed to a life of timidity and indecision.

By 16, teens should be drinking coffee on a regular basis, if only to appear more sophisticated. They also can enjoy the added benefit of caffeine during all-nighters.

Some pseudo-grownups foreswear coffee for health reasons. Instead, their morning beverage of choice is something insipid, like green tea, or juvenile, like Mountain Dew.

But I had to accept the health excuse. If they thought coffee would put them in an early grave, I had no choice but to bow to that explanation, while making a note to myself that, even if coffee ultimately shaved a few months off my life, it would be worth it.

But no more bowing. Fear of premature death no longer is a valid excuse for not drinking coffee (not that it ever really was).

Researchers now offer virtually airtight evidence that coffee is not only harmless, it’s also actually good for you. A study of 400,000 people, the largest study of coffee drinking ever conducted, suggests that coffee drinkers are a little more likely to live longer than non-coffee drinkers.

Regular or decaf? It really doesn’t matter, say the researchers.

And why do coffee drinkers live longer? No one really knows for sure.

According to the report, coffee contains a thousand things that might affect health, from helpful antioxidants to minute amounts of substances linked to cancer. And with all those variables in a cup of joe, scientists can’t pinpoint which elements or combination of them might be responsible for helping people live longer.

But while they can’t say why, researchers found that coffee drinkers were less likely to die from heart or respiratory disease, stroke, diabetes, injuries, accidents or infections. No effect was seen on cancer death risk, though.

Of course, some of the positive effects can be negated if people load up their coffee with cream and sugar. Coffee can’t protect you from diabetes if your shoveling three teaspoons of sugar into the cup.

By the way, I have been tempted to dismiss adults who drink their coffee heavily laden with cream and sugar. In a way, it’s cheating, turning coffee into something resembling hot cocoa.

Ideally, coffee should be drunk black to fully savor not just coffee’s deep chocolate and caramel aspects but also the pleasant bitterness that makes coffee ... coffee.

But I have decided to be charitable to those who doctor their coffee. At least it’s coffee, not soda or tea.

I also allow for cream in iced coffee. In fact, it’s almost necessary. But I offer the caveat that iced coffee is almost another drink altogether, as different from a cup of hot black coffee as iced tea is to hot tea.

I am pleased with the news that coffee could prolong my life. But I would have been satisfied to know that it won’t shorten it.

Coffee already offers enough benefits without having to make the roster of health drinks. Something that tastes that good and also provides a morning wakeup jolt is good enough for me.

Some people complain that coffee is too expensive. But that’s because they’re buying it at places where people sit around ignoring each other while they browse their laptops and tablets.

My advice: Make it youself! Even the most expensive pound of coffee will yield cups of coffee for only pennies apiece, nothing like the $6 mochalattefrappucino from the coffee shop.

And buy a grinder so you can grind your own coffee. That way, you can buy whole-bean coffee, which stays fresher longer and tastes better when freshly ground.

But by all means, if you’re 15 or over, drink coffee. Why bother to try to pass yourself off as a real adult if you don’t?

And, hey, maybe you’ll live longer.