Early life (1980-1992)
Max often uses his siblings' situation to his benefit. For example, when Alex used magic to go to the Crazy 10-Minute Sale, Max used that time to tell his dad, Jerry, that he had broken his wand. Max is shown to have a C+ in Wizard Class which makes him average. He has a few strange habits such as putting marshmallows with aspragus and he uses his mom's dress as a Darth Vader cape. In fact this unusual way of thinking allowed him to outsmart (or as Alex said "out-dumb") a genie into undoing her twisted wishes.
It is unknown if Max has lived in Waverly Place his whole life but it is known that he has Hispanic heritage from his mother's side. His mother often tries to get the kids to learn about their Latino heritage. From his father's side he inherited his wizardry skills. It is likely that he is also half Italian from his father, due to the last name Russo and the fact that Alex has stated that they are only half Latino.
Hogwarts years (1992-current)
Max was sorted into Hufflepuff during his first year at Hogwarts. He has managed to complete the first three years without much incidents.
Personality and traits
At 16, he is the most mischievous, determined to take his magic "to the Max." When he's not dodging homework and vegetables, Max plays practical jokes on his siblings. His first spell (on the show) was "Comakus Pancakus" to conjure up a stack of pancakes.
It is very hard to tell at times if Max is eccentric, outside the box or just stupid. He takes almost everything said to him literally, often confuses the meaning of words (such as aunt and ant), doesn't seem to understand when he's being insulted even when told he is being insulted, and has been known to do some very idiotic things such as shrinking his own brain just so he can store more jelly beans in his skull. However he has been shown to be an average level student despite his intellectual shortcomings. In the season 4 premier he claimed to be acting dumber than he really was so no one would believe him if he revealed he was a wizard.
His dumb personality makes him very innocent and simple. It is proved multiple times. During most problems and troubled times, he doesn't get even the least bit sad. Even when his siblings got to keep the powers, he was happy about being a mortal, basically because he never used magic and it wasn't as important to him.
Max and Justin are usually arguing or correcting each other's ideas. Justin is constantly yelling at Max for doing something stupid, or correcting his mistakes. Although, in Back To Max, Justin was very happy to see Max, and they get along as brothers.