I am reviewing the Japanese version of the show, which does contain some alcohol use, mild violence and the occasional use of bad language, sometimes in "Engrish". Still, I'd say it's definitely on for kids 8 and up, and at the age of 22 I still enjoy the show. The characters are engaging, and Sonic provides a great role model, if a little laid back.
I strongly recommend everyone to find the superior Japanese version with English subtitles online (or the French version which is almost identical to the Japanese one), instead of the vastly inferior 4KIDS dub. In my opinion the 4KIDS dubs simply dumb down their shows way too much, literally insulting the intelligence of the kids.
I think the Japanese version of the show is an excellent anime for its genre and perfectly suitable for kids 8 and up, and also enjoyable for people of all ages. Kids below the age of 8 could watch it, though that would depend mostly on the child whether they'd need adult supervision due to alcohol consumption and the occasional swear word.
Keep in mind, this is the Japanese version of the show I am reviewing. If I were reviewing the 4KIDS version, I'd give it 2 stars and an age rating of 0, and would add that it shouldn't be watched by anyone OVER 8.