Completely personal choice.

My DD didn't have any chocolate until she was a little over 1yr old, and then it was only a very little.

My DS1 would have probably been around 9months, but it was only a very little and only occaisionally - usually if his sister was getting a little.

My DS2, I am embarrassed to admit, his first food (at the ripe old age of 4 months) was a milky way. Curtesy of his big brother who thought he was doing the right thing by sharing. He has eaten alot of crappy junk food in his short life. Whenever someone has anything, he is there scavenging.

The way I figure it is that if the majority of their diet is made up of nice healthy foods (ie, food and vege) the occaisional treat isn't going to hurt them no matter what age they are. I completely respect parents who choose to hold off on these types of food as long as possible, but for those who choose to allow junk food early (or have that choice taken away from them), well, that doesn't really matter either - It is the bulk of the child's diet that is important. I try to always respect other parents rights to feed their child as they choose. The only time I ever might say anything is if the parent is mistaken in their belief that a particular food is healthy, when it is in fact not - but so long as they are aware of that fact, then it is still their choice.