The kids could be 27, but you should know that
2 person "Jet ski" in NH has a 16 year age and certification requirement. (You can't be under 16 and drive with an 18 year old with a cert)
Other restrictive rules.
http://www.boat-ed.com/nh/course/p4-...spectopwc.htm\
3 person "PWC" is more like a boat.
http://www.boat-ed.com/nh/course/p4-3_whomayoperate.htm
Under 16 can drive with a certified 18+ on board.
A 16 or greater needs a certificate to drive.
P.S. The kids will love it no matter what age.