What rights does a contracting minor have upon reaching the age of majority?

Hypo 1: Timmy is 17 years old. Timmy signs up for a gym membership. The terms of the contract state that Timmy must pay $50 per month, every month, for 1 year. Timmy pays $50 per month, each month. 4 months into the contract, Timmy turns 18 years old. His parents make him start paying rent. Timmy realizes he can no longer afford the gym, so he tells the gym he would like to terminate the contract. Result: Timmy signed the contract as a minor, which gives him the right to disaffirm the contract within a reasonable time. So it is his right to terminate the agreement.

Hypo 2: Timmy is 17 years old. Timmy signs up for a gym membership. The terms of the contract state that Timmy must pay $50 per month, every month, for 1 year. Timmy pays $50 per month, each month. 4 months into the contract, Timmy turns 18 years old. At this point, the gym realizes it can increase its prices to $100 per month. The gym sends Timmy a notice that because he is now an adult, they are terminating his contract and offering him the ability to sign up again at the higher rate. Result: This is not allowed. Only the minor has the ability to disaffirm a contract when they reach the age of majority.

Hypo 3: Timmy is 17 years old. Timmy signs up for a gym membership. The terms of the contract state that Timmy must pay $50 per month, every month, for 1 year. Timmy pays $50 per month, each month. 4 months into the contract, Timmy turns 18 years old. Timmy continues to pay the $50 per month for 2 more months before realizing he cannot afford it. He calls the gym and asks to cancel. Result: Timmy likely cannot terminate the agreement because he waited too long. He already paid for 2 more months, which would be evidence that he affirmed the contract and agreed to be bound to it as an adult.