I don't even think you need to "work out hard", just don't eat so much, walk more during the day and take the stairs whenever possible. Which reminds me. I am in my 30s but I am taking classes at a local college. When I get off of work there is a time gap between end of work and start of class so I sit in a very nice lounge in the lobby of the building where my class is held, relax and read. There is an elevator in this lobby in a building that is 3 stories tall because of handicapped access. Guess how many handicapped I see get into this elevator? Now guess how many fats?  The stairs are right next to the elevator, RIGHT NEXT TO IT!!! I am amazed at how long these fatties will wait for an elevator to go from the 3rd floor, to the 1st, so they can hit the 2nd floor. The icing is when they press the button, walk PAST the stairs to the vending machines, buy some beetus juice, then walk back after missing the elevator to press the button and wait again. The trip to the vending machines and back is the same distance of traveling up the stairs.