Most chat websites are only for 13+. There is a REALLY important reason for this- there are people out there who try to meet up with young people and cibai harm them.
it is very easy to lie over the internet (for example some under13s join websites where it says only 13+). I really advise you don't use ANY chat sites. However, I'm not sure of the age restriction on MSN but it has pretty good instant messaging. :-)