Is 120 overweight for a 12 year old boy?

It is not possible to answer your question. There is no perfect or ideal weight for a 12-year-old male (or a person of any age) because weight is related to height and body compositionrather than age. For more information, and to see the growth charts or learn about the causes of unwanted weight gain, see the page links, further down this page, listed under Related Questions.