BASA uses the USA Swimming Age Group Motivational Time Standards (see link below). These standards are updated every four years and are calculated from actual times swum by USA swimmers over the four year period. The attached standards document shows age group standards (10 & under, 11/12, 13/14, 15/16 & 17/18) for boys and girls for Long Course meters (50m pool), Short Course Yards (25 yard pool) and Short Course Meters (25m pool). The standards are labeled B through AAAA with AAAA being the fastest.
For more BASA Time Standards information click here.