Have a good head on your shoulders
Definition 1 of 1
Pro Tip 1/3Positive Connotation
Describes a person with clear, rational thinking and good judgment. 
Despite his youth, Tom has a good head on his shoulders.
Pro Tip 2/3Not Literal
It means being clever and sensible, not the physical head. 
I trust Lily to plan our trip; she has a good head on her shoulders.
Pro Tip 3/3Maturity Implication
Often suggests the person is mature beyond their years. 
Kyle's only 18, but he has a good head on his shoulders, managing his budget well.