I would pull back the foreskin, and attach the device to your shaft just below the head. In my post, I said I was having difficulty with the placement of my head strap. All my knowledge has come with experimentation. Use the noose if you want, or get the x4 quad support. Increase your knowledge and read more on the topic. There are options just remember when it comes to extending you are stretching your tunica and shaft skin, not your dick head or in your case your foreskin.
I extend in sets of 20-30 minutes with a 5 minute reheat in between sessions. I have never attempted to extend all day; however I plan on buying the Modified VacExtender which would allow me to.
In my experience, heating while extending and other devices have been very beneficial. Make time every day to enlarge your penis. I use an electric heat pad that you can find at CVS, and wrap that around my extender when in use. I also bought the Bathmate Heracles Edition, and I use that consistently as well.
I'm 18 too and I hear you there on seeing other guys my age with bigger bulges. I'm new to this penis enlargement, maybe we can help each other and try out new exercises. see what benefits the most for our age. Let me know