Responding to hypnosis is like responding to a placebo. Placebo responsiveness and hypnotizability are not correlated. People with certain types of personalities are likely to be hypnotizable. There are no substantial correlates with personality measures. People who are hypnotized lose control of themselves.
Subjects are perfectly capable of saying no or terminating hypnosis.
Age-regressed adults behave like adults playacting as children. A person's responsiveness to hypnosis depends on the technique used and who administers it. Neither is important under laboratory conditions. It is the subject's capacity that is important. When hypnotized, people can remember more accurately.