I'm not sure focusing on one thing (cycling) is the best plan, it's a lifestyle change really. I got skinny by becoming more active in general (swimming every day, taking up hiking, cycling came later, and generally walking places and keeping on my feet – I don't bother really counting any of this). Of course, exercise in itself will only burn so many calories and on its own unlikely to result in significant weight loss (though being healthy and fit has so many other benefits and I think it really helps keep weight under control). Which leaves diet. I dropped all the junk and processed food, cooked quick and simple things, heavy on the veg, low on the carbs (without being obsessive about any of it). Turned out to be lot tastier than a plate of oven chips and a pie. Also, and this is a biggie, dropped snacking. A couple of biscuits or a chocolate bar can easily add a lot of useless calories. Sugary soft drinks too, probably the worst way to get unnecessary calories ever, you can achieve the same effect more cheaply by thumping yourself repeatedly in the pancreas.
I think most gyms these days have a far wider range of clientele, certainly my gym and pool runs the gamut from svelte young things in lycra to gurning grannies.