Ok, a bit of honesty here. If you're that out of shape at your age that a very good sign that you need to exercise. The body needs exercise to function properly.
Start slow with just walking or riding a bicycle a short distance and gradually work up from there. 20 minutes a day is a great start.
How many times a day do you eat? The best way to boost metabolism is to eat several small meals a day instead of just one or two larger ones. Of course eating the right foods helps, but spacing your food out through the day goes a long way towards keeping metabolic rates up.
It's really a very simple formula. Burning more calories than you take in causes weight loss. Taking in more than you burn causes weight gain.
At this point I'd be more concerned about you being so out of shape than with your weight. Get yourself a bicycle and start riding it. I love riding a bike and do so as often as I can manage.
I have a recumbent bike at home which is my only transportation when home off the road, and I carry a folding bicycle in the truck with me.