I always thought that CSI's are primarily scientists who undergo training as a secondary requirement -- so that they know what to do in case the perpetrator/suspect is still in the crime scene and they get attacked... think about the season ender of CSI...
Nick got abducted because the accompanying police officer had his back turned.
Some of them, though, start out as cops and eventually get into forensics. I'm guessing that's why some of them have "detective" for titles.
Is
Grissom called a detective? (this is not rhetorical, i'm really wondering!)
Speaking of
Grissom, remember how he always says that he's a scientist; not a cop?
And look at
Horatio... he's more of a cop rather than a scientist.
I think
Danny's more of a scientist. Otherwise, he wouldn't have screwed up so much in
"On the Job." So that would mean four or even more years of college (depending on the degree he got). I think he's about 29-30