Is it “safe”? Yes, compared to cities of similar population around the world, Amsterdam is one of the safer cities.

Is it safe for you? I dunno. Depends how risky your behaviours are. If you seek out dark back streets in the wee hours, then it might not be as safe as hanging out around the Dam in broad daylight; (the Easyinternet cafe nearby warns patrons about pickpocketing, btw).

Is it safe for a 17 year old? Depends on the 17 year old. If you’re a loud-mouthed obnoxous twit looking for trouble, then it’s probably not very safe. If you’re level-headed and confident, then probably won’t be much problem.

Stuff can happen anywhere but to me Europe is a very safe place.
I personally do not think 17 is too young; doesn’t look like the Sensation events have any kind of age restrictions either. (I have seen plenty of irresponsible travelers who were a lot older than 17.)
It’s good that you plan on going with or without your friends, sometimes people back out of things like that. In the meantime you can save money, and research Amsterdam and perhaps some other places.
Recently, Oldlady posted about travelers under 18 needing written consent from their parents. This was news to me, but I guess this just happened in the last few years. Here is some more information about it.
Minors travelling internationally

I’d go with 17 is okay.  Before my first trip, I was told that I’d enjoy it because it’s so much safer than here.

and another bonus is you only have to be 16 to play in the red light area. According to a friend on mine who worked for contiki they used to advise guys that if you want to bang a hooker Amsterdam is the safest place in Europe to do it.