I could grow a full beard at around age 17 so I used to always have a bit of scruff... or I would only shave every month or so to keep it tame.

Now that i'm 20 and in college I like to look cleaner cut... I went from shaving every week this last summer, to shaving every other day. Every day is a bit too rough for me... I have sensitive skin as well. However no matter what I have kept some sideburns that go to the bottom of my ear.. so mid way. It compliments my shaggy hair (3 to 4 inches long)
To help prevent razor burn, go WITH the grain (the way the hair grows)... when you go against it, it irritates it and can make red little bumps that hurt. I also use Nivia Men aftershave lotion.... it really helps. Especially since it's getting cold. OH and if you use a dull razor blade... it will irritate your skin more. So after every 6-10 shaves (i dont count), I will change razors.. so every 2 to 3 weeks I change it.
I prefer the Gilette Mach 3 turbo with the 3 blades.......

I'm talking about shaving my pubes bro.