here are the guidelines for nutrition.
a ten pound cat should be eating 280 calories per day, not sure about a kitten but its on the scale.
is you kitten eating a good quality food with high protein and NO grains?
how much is he eating and what does he weigh?
http://docs.google.com/viewer?a=v&q=cache:gKVSh9ouQbsJ:dels.nas.edu/dels/rpt_briefs/cat_nutrition_final.pdf+cat+nutritional+requirements&hl=en&gl=us&pid=bl&srcid=ADGEESg2MiLE93GTFmVqjZOowsnx22qePvjZAlh4HXekub6Mkw_vWeHQb4Um318LaH6fCpEw6GKxiufO7pjVf4pODqWGxvK9ziH_09yyQ7YEA6NV2_fj0Snvfwbm5S7UIJssqEdt-9kp&sig=AHIEtbTmhy6eknR0gpxmsnqiOYPdMQdMTA
Growth and weight gain slow substantially when a kitten gets to be about 6 months old. For the first 6 months they gain an average of a pound per month, and they may only gain another pound from 6 months to a year.
Do you know how much your cat weighs? If she is healthy, she may just be a small cat.