The wetsuit rules change by race and governing body but the general rules
for ITU races are:


Elite athletes in the Olympic Games and ITU Events:
Swim Length  Forbidden above: Mandatory below:  Maximum stay in water
1500m   20 deg. C   14 deg. C   30 min
1500-3000m 23 deg. C  15 deg. C  1 h 40 min
3000-4000m 24 deg. C  16 deg. C  2 h 15 min



Junior and Age Group competitors:
Swim Length  Forbidden above: Mandatory below:  Maximum stay in water
1500m  22 deg. C  14 deg. C  1 h 10 min
1500-3000m 23 deg. C  15 deg. C  1 h 40 min
3000-4000m 24 deg. C  16 deg. C  2 h 15 min



And for USAT races are:


"Each age group participant shall be permitted to wear a wet suit without
penalty in any event sanctioned by USA Triathlon up to and including a water
temperature of 78 degrees Fahrenheit. When the water temperature is greater
than 78 degrees, but less than 84 degrees Fahrenheit, age group participants
may wear a wet suit at their own discretion, provided however that
participants who wear a wet suit within this temperature range shall not be
eligible for prizes or awards. Age group participants shall not wear wet
suits in water temperatures equal to or greater than 84 degrees Fahrenheit.
The wetsuit policy for elite athletes shall be determined by the USAT
Athletes Advisory Council."