I am not as old as Brad Pitt but getting there, and while my "window" has widened as I get older it's not so wide. Married now but if we were still doing the recreational sex I would say about 10-12 years in either direction for casual (as long as there is mutual attraction) but for serious dating my husband is almost 3 years older than me and that's about as wide a gap as I would be comfortable with, my preference is same age. My kids say I seem much younger than him already, lol, but I don't think that is years.