The first thing I could grow was a mustache freshman year... and I was so proud of it. But it looked horrible. I was made fun of so bad, and I'm sure all the girls though it looked gross. I shaved it after a particular blunt day of jokes at my expense, and have never grown one since. Senior year of HS I started growing a bit of a chin-strap, and I have kept it so far. I like it and so does my GF, but I am thinking about going back to clean shaven. The problem is that it makes my jawline much more pronounced, which looks good.
I'd say no on a mustache though, they rarely look good
Around grade 9 it became noticeable that I had to shave, the mustache came in mostly first.
I Usually stay clean shaven or a little stubble/5 o'clock shadow because it's a hassle to constantly shave every day. I do it about every 3 days anything longer it looks sloppy and it hurts to use an electric razor.
The usual, slow signs some time before 18, gradual increase over the years. I never got to a the point of a full beard so it looks like ass if I don't shave what's there. I'd get it permanently removed if I could since it serves no purpose.