The bottom in this scene was featured two months ago here on the blog, where the photo set is still available for downloading. This scene is labeled as "part two" but is complete. There's never a conclusive way to prove a lad is a virgin, but this scene allegedly features him losing his anal virginity to a man.
This scene may not last long on the source webpage, so if you can't view right this minute, download a free copy to enjoy at your leisure. The original video and download link are located here.