Is it possible that the increased aggression of my child is the result of increased testosterone in the blood?

Unlikely: It is unlikely that the aggression in your child is due to increased testosterone unless he is taking a supplement containing testosterone. Excess testosterone would manifest itself in younger children with usually more rapid growth and skeletal maturity in addition to other signs of early mascularlization.

Yes but unlikely: Aggression is not usually driven mainly by hormone quantity, but by a complex mix of emotional, psychological, spiritual and possible physical triggers. Persistently seek help from a team who can consider and work with these components as they apply to your child, and keep your child and those around the child safe.

Highly unlikely: There are precious few scenarios in which that would happen and all of them are exceedingly rare. It's likely you have a combination of a boy, who is very active, maybe some behavior and discipline issues tossed in.