An inexperienced kid not fully prepared to play an instrument

• Tyro with a colorful instrument?
• Like sprouts and maize, hot not cold, for a starter
• An awkward and inexperienced youth
• Inexperienced sort
• Half of Paul's dilemma?

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM OTHER ENTRIES ▪ The greenhorns headed out to the corral for their first ride.

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
mid-15c., "young horned animal," from green (adj.) in sense of "new, fresh, recent" + horn (n.). Applied to new soldiers from c.1650; extended to any inexperienced person by 1680s.

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Greenhorn \Green"horn`\, n. A raw, inexperienced person; one easily imposed upon. --W. Irving.

Wikipedia Word definitions in Wikipedia