This happened to me 6 years ago- the summer I turned 19.
As a teenager, I had a grown from admiring and jerking off to hot girls in porn, to slowly becoming jealous of them wanting to BE them, instead of wanting to fuck them. This fantasy grew into some experiments with lipstick, panties, and stockings during my later teens - but never more than that. However - everytime I jerked it to porn- i was picturing myself as a girl on her knees sucking dick and getting fucked.