Dual Meet competitions are organized by the coach where a line up is put together and separated by gender and age groups.  It is posted the day of the meet. 

AMS is organized by qualifying time standards as well as gender/age.  Fir each AMS meet, the meet host will publish an invitation with a list of qualifying times and available events. 

In dual meets as well as AMS/USA Swimming meets, the age group entered by a swimmer is determined by the age he/she is on the first day of the meet.  The age qualifications are typically as follows, although AMS/USA Swimming meets can vary:

8 years and under

9-10 years

11-12 years

13-14 years

15 and over/senior