how old do you have to be to ride kayak?

I'm not 100% sure but I believe 16 yrs old.

RANKIN LAKE BOAT RENTAL POLICIES: A person must be at least 18 years of age to rent a boat.  Sixteen and seventeen year-olds may take a boat out, but a parent or legal guardian must be present to sign the rental/release form.  A child between the ages of 11 and 15 may be in their own kayak/canoe, but only with adult supervision in another kayak/canoe, within 100 feet, on the water.  Children 10 years old and younger must ride, in the same vessel, with someone 18 years of age or older. The renter’s Drivers’ License or valid state ID is required as a deposit for each boat.  It is the RENTER’S responsibility to pick up his/her license after the rental.