Damn right they are. Problem is finding the consistently good ones. Hormonally, your body starts peaking in the early 20's (sometimes earlier, sometimes later depending on the individual). Many of the really good ones , like growth hormone, start falling rapidly. I've read in a few places that it decreases 50% every 7 years after age 20. Same for other things like testosterone too. So growth hormone precursers and testosterone precursors (like androdiol) become important for gains. And then there are the 19-nor-androdiols - all the building blocks for the liver to turn into steroids. AS far as protein suppliments, if you want to make real gains in muscle size and mass, you will be hard pressed to do it on regular foods - you'll get sick from overeating.
Now, I am 50 and have been working out regularly. 4 weeks ago, I decided to try competition this June. So with little changes in exercise program, and lots of supplements, I have made "visible" progress in the last 4 weeks (and when I can see changes in myself they must be significant). I'll be starting to diet down in another few weeks, and suppliments will be of prime importance in dropping some 40 pounds in 13 weeks while maintaining muscle mass.
If you are in your late teens or early 20's suppliments are not as important. If you want to stay fit and toned, they are probably not necessary at all. But if you want to become BIG and LEAN, it will be far easier (at any age) with suppliments. In my opening statement, I said something about consistency. Go with the name brand products like Cytodyne, Biotest, Met-Rx, EAS, etc. They have stringent quality controls in place so yo uknow what you are getting. I have tried some off brand stuff that admittedly was worthless.