......cause he is 18, and learning ,exploring......

Exactly!!!!!!!
when I was shooting my canon fd stuff back in the day, I just had to have a fisheye. I picked up a used Vivitar series 1 lens and had a blast with it for a couple months....BUT....shooting special effects with that lens led me to special effects infrared, both color and B&W, which I shot for years....so had it not been for the fisheye I may have never got interested with infrared.....
sometimes shooting with a fisheye can make you get in real funny positions, so a Right Angle Finder can be useful. I believe you can pickup one new for 70-80 bucks
BTW, the 2 lenses I listed, just because their "cheap" at 250.00, from what I understand both are very sharp!
I just picked up a Nikon 10-24 and cant wait to try it out, and now looking for a right angle finder because I'm sure I'll be shooting a lot with it, just a few inches from the ground..lol
tell him to go for it!!!