Is 64 lbs healthy for an 11 year old boy?

it really just depends on how tall you are and your family history. if both of your parents are fairly slim and don't weigh that much, and you are, say, 4'10'', then no you aren't too underweight. another good way of figuring this out is checking out your bmi : usually under 19 is considered "unhealthy" or "underweight". u can easily check your bmi over the internet: just google 'bmi calculator' and click on a link.