It all depends on what you picture as 'fit.' If you want a six pack you might have some difficulties. If you want to be fit like in a world where not everyone is a fashion model, grab a pilates ball for some abs and back stretching, use the stairs and try to walk twice a week. Add some push ups if you want, and a whole body stretching routine. This takes around 30 mins including warming up. Don't eat junk food and drink alcohol more than once a week, this makes you fit automatically. If you go for defined muscles you want something else other than to be fit. Pump iron and destroy your knees by going running. In a few years you'll most likely remember those who would tell you 'how good' sport was for your body.