So it's not exactly the same. For people who have very little free time due to commute, work, children, etc. It's harder to spend half an hour of free time a day on exerciaing.
I mean I do agree with the premise that exercising is a good return (especially since the better sleep quality should be factored in) but I think the person you're replying to has a point when he says that saying it's one year of life is not really comparable
I mean, we all know of the university budding sports star types who probably invested in many hours training and trying to break into their sport professionally but not quite cutting it - and then "retiring into mediocrity" with the regular 9-5,2 hour commute, 3 kids and the diet to match. They exercise no differently to the regular Joe and suffer all the maladies the same.
We use this sort of formulation everywhere. If I say I work 40 hours a week, no one is going to assume that I start work at 9am on Monday, work non-stop until 1am Wednesday, and then take the rest of the week off. If I say that people spend approximately a third of their lives sleeping, no one thinks I mean that they sleep continuously from birth until they're 30 years old, and then spend the next 60 years awake.