There are three competition divisions within AQHA shows: open, amateur and youth. Read on to learn more about each.
Open
If you have a current AQHA or AQHYA membership, you are eligible to show your American Quarter Horse in open competition. Open competition is usually for the most experienced exhibitors, trainers and professional horsemen but many amateur and youth members can be tough competitors as well.
Open classes can also be divided according to the age of the horse.   

• 2-year-olds
•    
• Junior horses (5 years of age and under)
•    
• Senior horses (6 years of age and older)

How It Works
Within the open division are levels: Rookie, Level 1, Level 2 and Level 3. These are based on the horse's achievements.
For open division halter and cattle events, classes are leveled by the exhibitor's record. Those levels are: Rookie, Level 1, Level 2 and Level 3.
To learn more about these levels, determine your specific level and find out how the levels group horses and riders with similar skill and experience levels for competition, visit www.aqha.com/leveling.
Eligibility
If you are a paid professional and you are ready for a higher level of competition, then the AQHA open division is for you!
Amateur
American Quarter Horse owners who do not join the professional ranks may enjoy a full spectrum of competition in the amateur division.
How It Works
Within the amateur division are levels: Rookie, Level 1, Level 2 and Level 3.
To learn more about these levels, determine your specific level and find out how the levels group riders with similar skill and experience levels for competition, visit www.aqha.com/leveling.
Eligibility
You may obtain an amateur membership if you have not shown, judged, trained or assisted in training a horse (whether or not a registered American Quarter Horse) for remuneration, monetary or otherwise, either directly or indirectly, nor received remuneration for instructing another person in riding, driving, training or showing a horse for three calendar years previous to application for amateur membership. 
Amateurs must exhibit a horse in their ownership or in the ownership of someone directly related to them (see AQHA Rule SHW220 for details). The relationship of the amateur to the owner of the participating horse must be evidenced by submitting legal documentation (i.e., copies of marriage and/or birth certificates) to AQHA's Show Department.  
Every person competing in an Amateur class at any AQHA approved show must hold an amateur membership and be 19 years of age or older on or before January 1 of the current year.