How is it possible that heterosexual males have more sexual partners than females--start younger, do it more, or hang in older?

Not possible. This is hilarious. It's not possible. Either men are lying and saying they have more partners or women are lying and saying they have fewer partners. This article explores the discrepancy: http://www.Nytimes.Com/2007/08/12/weekinreview/12kolata.Html. One explanation is that maybe some of the mens partners are imaginary.