There are two ways that max can be used as a noun. Max, in itself, is not a real word. It's slang for Maximum. To use it in a sentence as a noun could be: Timothy pushed his brother's patience to its...
Max is about 16. He got left back in 7th grade twice, that would make him 15 and it has been a year since Freak died. Even though he is in the 8th grade, he is 16.