This is the age your metabolism slows down and you start putting on weight
Remember when you were growing up, you could eat what the hell you wanted?
Every school day you gobbled down chocolate and gulped down pop and you stayed lean as a whippet.
But now if you so much as look at a plate of chips, you bloat like a pufferfish.
There's a reason for that. When your parents told you that one day your metabolism would slow down, they weren't joking.
When you reach a certain age your body's calorie needs peak and after that you need fewer and fewer calories to maintain weight, according to UCLA statistician Nathan Yau.
That's not necessarily a problem if you're eating less and less food at the same time.
But if you're still eating like a horse - powering through bottles of coke, snacking on doughnuts and still eating three huge meals a day - then the law of calories in/calories out dictates that you will put weight on.
The graph, from the US Department of Health, below basically shows how much less food you should be eating ever years as you age and was published on Yau's Flowing Data blog.
Men who are active (doing more than three miles a day) see their calorie need peaks around the age of 18 or 19 at 3,200 calories. The metabolism slows slightly at this age, with drops of 200 calories throughout their 20s and into their mid 30s when it drops again by 200 calories.
Men doing moderate activity (so one to three miles a day) can quite happily maintain their bodyweight on 2,750 daily calories from their mid teens to their mid twenties.
But that metabolism starts slowing when you hit 25 by around 200 calories.
For men who are sedentary (no daily exercise and lots of TV and sitting at a desk) peak in their early twenties when their metabolism starts slowing and their body only needs around 2,400 calories. And it keeps on dropping with age.
This gives you a very clear idea of when you need to start curbing the booze and takeaway binges.
Interestingly the grey bars on the graph show men's actual food consumption - and what you'll notice is active people aren't eating enough, while sedentary guys are eating way too much.
It's a similar story for women, except you'll notice calories remain a lot more constant...