Gees, this is not a competition I hope.
First of all, the past is well.....the "PAST". For better or worse, it's history. Can't change it, just learn from it.
Second, having a zillion previous partners is actually a negective thing. It might be something the college jogs brag about but certainly not what a responsible adult would consider a plus. (not to consider the risk level of STDs on top)
Last, most of "the past" is in the past because along the way something went wrong! Or else it would be "the present"
And everybody should have the right to keep their skeletons in their own closets unless they volunteer to clean it out.
Curiosity is normal and good, but the subject is wrong. Too often people ventured into these areas thinking they can handle it but later found out they Can't. So do try to steer clear of past ex as conversation subjects. Really, it doesn't do ANYTHING going there.