When does a kitten start to eat solid food?
by KittyKondo.com 

     From the age of 10 days to three weeks a kitten starts to experiment with eating solid food and will spend a minute or two a day attempting to nibble. It will usually try to eat anything it sees it mother is eating. At this stage it might be a good idea to start introducing wet cat food by putting a little bit on your finger tip and allow the kitten to nibble and get used to the scent.

     Anywhere from three weeks to 14 weeks of age kittens will spend about 30 minutes per day eating solid food until it becomes part of their entire diet.  If you're trying to introduce hard food to a kitten you should first mix in dry and wet foods to get your kitten used to chewing on the harder stuff.