I'm 39 years old, 6' and been working out hard 4 months. I have seen significant gains with a 3 day split that I do twice each week and eating more and tons of protein. I've went from 160 to 180 lbs in those 4 months. I've gained muscle and definition but have been on a bulk mind set before I cut. My knees are starting to hurt a bit from flat feet and rapid mass increase.

How do I know the sweet spot to start to cut body fat? Summer is on the way, but I don't that to make my decision solely.