Aaah but you guys are still Young......
When i was your age(s) i was never doing much sporting exercise,(except playing for the local football team),I tended t oget most of my exercise from walking everywhere.
I've always watched what i eat,but as you get older and your lifestyle changes so too will your eating habits as your body slows down
I have always had a healthy weight,and guess i'm lucky that i have stayed in shape,when most of my friends I grew up with are lazy (some of them overweight),the thing is as you get older,you have to work harder to keep your figure,and believe me it will be even more hard work if you never looked after yourself in your youthful years,
I'm 32 next month,i still maintain a youthful look compared to many of my friends the same age,I do feel my age mentally but definetly not Physically,I'm still as active as i ever was,infact even more active than i was in my youth...and that,I put down to keeping myself active through exercise,discipline and balanced diet,it can be hard work,but you need to look at the bigger perspective it can be so much more comforting to do nothing,but as life gets harder as you get older so too will maintaining your bodys everday faculties that we all take for granted...
Most of my mates would rather spend a few hours down the Pub drinking themselves into an early grave and eating unhealthy food,yet always complain they have no energy to do anything or have no time to go for a run or swim!!!Yet they manage time for a couple of beers!!!
If you make an effort ,then your body will thank you in the long run...I've always said that if you keep putting the wrong grade of fuel into your engine,without proper and regular maintenance sooner or later you gonna break down...or die in certain cases!!!
Working whole my life to loose weight but it's so difficult. 
