Hmmm...

First "real" girlfriend (I was 16-17). She was older, went off to college, cheated on me. Broke up in Septemberish...? Probably was over it for the most part by early winter. Began dating new girlfriend a few months later.

Number 2 (17-20): Dated for over 2 and a half years, broke up at the end of sophomore year in college when she admitted she just didn't love me any more. Ended up hooking up over the summer off and on after breaking up. Continued for a bit into junior year, finally stopped when I got a girlfriend around maybe October...?

Number 3 (20-21): Dated until the end of summer right before senior year. I broke up with her because I knew we wouldn't work out... living together really opened my eyes to us not clicking. Didn't get another girlfriend in college, but dated several (and hooked up with this ex) throughout the year.

Number 4 (22-23): Dated a younger girl I met while volunteering for the 2008 political campaign. We broke up the next fall when she cheated on me with a classmate. We continued hooking up for several months after anyway. Lasted for about a year until I started finding new girls interested in me, including one who became my next girlfriend.

Number 5 (24, 25-26): Dated and broke up twice. First time I dumped her because I felt we were in two different places (I was working, she was a college student) and I was considering moving. We started dating again about a year and a half later when she was close to graduating and had matured a fair amount. Moved in with me after graduating, but broke up a few months later because she wasn't happy. Lived with me for a couple more months until she found her own place.

Number 6 (28-present): My current SO - together for over three years and currently engaged!

TL;DR: Usually took a few months between breaking things off completely and moving on to someone new. If I continued interacting up with them after the breakup, the timeframe to move on was quite a bit longer.