There are lot of studies that show that coffee extends life. Researchers are talking about all these benefits that include protecting cells from damage, reducing risk of diabetes, benefits for liver, reducing depression etc. etc. etc. But, what if all of those benefits indirectly stem from mental benefits of coffee. Coffee boosts your energy levels , it allows you to make faster and better decisions. In the long term, these things compound, you continuously make better decisions, which opens more doors, which yields health and life benefits. Long term coffee drinkers have better health, but we can't really say that it has direct health benefits.
>but... does it matter? as long as it makes you live longer...
Of course it does matter. First of all, if health benefits of coffee come from energy boost and better decision making, then someone who already has high energy level won't see benefits of coffee or even might have negative effects. Second, coffee might have negative long term health effects, which are being masked by mental benefits. If so, or people who need to stay alert and make fast and important decisions in their professional life, coffee might yield net positive benefits overall, but for people that have more harmonious life, net benefits might be negative.