The YMCA of the USA follows the USA-Swimming rules.  The current 2009 rulebook, which is in use for the 2009-2010 season reads...
 
Rule 102.9.1A for SWIMWEAR - "Swimsuits worn for all 12 & under age group defined competition shall not cover the neck, extend past the shoulder, nor past the knee."
 
So it would appear that the rule (which was passed in May, 2009) only applies to 12 and unders, BUT...
 
I copied and pasted the following from usaswimming.org and this seems to cover all swimmers immediately...
 

FINA issues initial 2010 list of approved swimsuits  (10/20/2009)

 

FINA has issued its first list of swimsuits that have been approved for use in competition.

 

The 2010 List of Approved Swimsuits, available here, is not all-inclusive and is not the final list. As additional suits are approved, they will be added to the list. 

 

Until such time as FINA publishes its final list, USA Swimming will allow all swimsuits meeting the criteria below, including those listed on USA Swimming's Reference List for Allowable Swimsuits in USA Swimming competitions.

 

The criteria for allowable swimsuits at USA Swimming competition, under Rule 102.9, is as follows:

 

1.      Swimsuits for men may not extend above the navel or below the knee and for women may not cover the neck or extend past the shoulders or below the knee;

 

2.      No zippers or other fastening devices are allowed except for a waist tie on a brief or jammer; and

 

3.      Suits must be of textile material and must not be made of any rubberized type of material such as polyurethane or neoprene.