My puberty got all messed up from ADHD stimulants for ten years. My dick was pretty much done growing by 17 or so. I always heard that penises can grow up through age 24 (around where I am now), so I maintained hope that my dick would naturally grow.
In erect size, I didn’t change much if at all. But one nice change I noticed in my early 20’s was that my package turtled less, often hanging almost impressively (where I’d look at it in the mirror, be shocked, hold it to feel its heaviness, etc - never EVER had this at age 18, always was turtled) and balls hang low more often, especially in the evenings. This also might have had something to do with me getting to a healthy body weight and becoming physically fit and more cardiovascularly strong.
I’d say go ahead and try it out, but read for a long time before you do. Being 18 means you probably don’t have exceptional experience with things like patience, true dedication, hell, you might not be able to truly grasp how ‘fast’ one year of time really is! (I’m speaking mainly for myself and how I was at age 18 - maybe you’re a better man than I was!).
What I’m saying is do a few months research at LEAST before you start. I’ve been reading these forums for a year and only just now feel like I have a decent grasp on PE and a good place to start. I got injured rushing into things, and had I known what I know now, I would have started so much differently, and probably never got injured.
So read up, young man, and enjoy still being in puberty! Also, while you’re 18 I highly recommend doing intense workouts like interval sprints (look them up on google), or burpies - or programs like P90X or insanity. Workouts like these drastically increase your HGH production (by 400% in many cases) as well as testosterone production - you want to do these things and get in the best shape that you can NOW, because NOW is the time that you’re still growing. With all that extra HGH and testosterone flowing through your system, you might get a little extra bone growth, hell, maybe even some penis growth out of it! If you do these things while you’re under 24, you still have a chance - any older, and you’ll just make yourself healthier and look better, but no extra skeletal growth.
I envy people who are fit their whole lives - things like wrestlers who’ve been wrestling since they were 5 years old - they get so much extra good testosterone and hGH their whole lives, and I honestly think they maximize their dick size in the process. Kind of went off the beaten path here, but just wanted to let you know that you’re lucky to still be in this critical window of development (albeit at the latter end).