I lost 150lb in 20months, so yes it is possible.
When I started I struggled to walk across a room, used crutches, couldn't get in and out of the bath myself, was I pain 24/7.
It's all about making lots of small changes over time. I started by simply logging everything (and I mean everything) I ate and seeing how many steps I took on average in a day.
After a week I plugged my details into myfitnesspal and chose a deficit, you do not need a huge deficit, 1lb/week is plenty. I also set my activity level to sedentary and allowed mfp and my garmin talk to each other to add exercise calories. I would then attempt to eat 50% of those calories on top of what mfp gave me as standard. And believe me the heavier you are the more calories you get to eat, I was on around 2000Calories to start with.
With activity I looked at how many steps I was doing on average and then tried to increase that by around 500/day each week.
Then after a couple of months I joined a gym, I was super lucky with that gym and the owner took me under his wing. At that point just moving was enough cardio, but I learnt to strength train and at the same time very slowly started to add in more cardio. To begin with I could barely manage 5min at 3km/hr on the treadmill, but over the months and years I built it up, started running and now have 4 marathons under my belt. I also joined some exercise classes, when I started I had to modify everything, 6 years later and I can do almost everything.
Throughout my weightloss period, I also set myself goals. Short term one's of losing 10lb, medium term one's of losing 10% of my bodyweight and of course my long term goal of losing 150lb. But I also set myself fitness goals, to be able to walk up a flight of stairs, be able to walk 5k, they were a couple of my original goals.
I'd also recommend taking progress photos on a monthly basis, sometimes the scales don't show the progress but photos do.