You have to figure that's at least 3-4 lbs a week, healthy weightloss is usually 1-2 lbs a week.
A lot of times when you first start you will lose a large chunk of weight, then gradually slow down till you get close to your goal, the closer you get the harder it is to lose those last few lbs.
Say you lost 2 lbs a week for 4 months, that would be 36 lbs, which I think is doable

60 lbs might take you close to 8-9 months. But who knows, the body does it's own thing- it might take you less, it might take more- I say just go for it and do your best!