It's going to differ wildly from person to person. But one thing that I would say is don't worry too much about not being optimally prepared for the start of your degree. When I started my maths degree after being out of high school for a while, I had literally forgotten how to expand (ax+b)(cx+d). I remember my TA thinking that I was joking at first, and then looking at me in horror as she realised I genuinly didn't know how to do it.
Needless to say, the first few weeks were a bit rough, but if you have the aptitude for it, it will come back to you quickly enough and you'll be caught up in no time. And you don't even need to do particularly difficult maths for CS. As long as you're hard working and don't have dyscalculia, you'll be totally fine.