To be honest, none of the five words/phrases you listed sound derogatory.  「若{わか}い連中{れんちゅう}」 might to a very small extent, but the rest sounds just normal.

The real question, to me at least, is: "Should you really use a derogatory term to refer to a group of millions of people?"  Not sure what the answer would be in your language and/or culture, but in Japanese culture, I can guarantee that that would be considered highly abnormal.  It is not like using a derogatory term to refer to a group of several that you personally know.

I would stick with 「若い連中」 myself.  If, however, you still want to know some derogatory terms for future reference, then we have:

・「若造{わかぞう}」

・「青二才{あおにさい}」

・「（くそ）ガキ」

・「ひよっこ」

・「鼻{はな}たれ小僧{こぞう}」

Somebody stop me!