Um…I’d be a little worried about you if you weren’t feeling temptation. I’m 38 years old. I’ve been tempted to think of naked women basically every few minutes for…let me see…about 25 years now. So, I have to keep my mind focused on other things, work, prayer, reading, writing, music…but occasionally my wife and I get to enjoy each other and there’s no need to think of anything else for a while. Life’s good!
From a religious perspective, do your best. Put your mind to productive things as best you can, if you find yourself entertaining some fantasy, clear your head and get on with life. If you really get off track, and realize you haven’t even been trying to behave, then we have confession. God has been listening to men confess letting their minds run crazy for 2,000 years now. He understands, since He invented this desire for His purpose of procreation in the first place. Also, really listen to the advice priests give you in confession. They have to learn to live celibate lives, so they know ALL the tricks for occupying their minds. A good, helpful priest can really give you some insight.
And, ultimately (and this is sort of mysterious I know) we need to thank God for our desires that we have so much trouble controlling. He set this task for us, and it seems impossible I know, but once you find your vocation it will all make a lot more sense - trust me! BTW, good job posting on here for help rather than giving up. I know that extreme sexual temptation that is SO hard to resist can lead to despair sometimes. Don’t let yourself get too bogged down, you’re normal, and you’re fighting the good fight, look at it that way.
ALSO - Although he was a Protestant, read CS Lewis’ “the Screwtape Letters”. Really helped me to understand temptation. There’s one chapter where a man is being tempted and it’s getting him down, then suddenly he realizes he’s being tempted and how silly he is being, and he laughs it off…I totally understood once I read that what Lewis was getting at. We are sort of silly and need worry less and trust God more to help us.