(a) That's wrong. Youthfulness, with its attendant lack of maturity and judgment, may, in some circumstances amount to a circumstance that would make a contract or other legal transaction voidable on grounds of unconscionable dealing.
However, for that to happen, the effect of the youthfulness must be such that it makes the young person (Sunny) incapable of judging whether or not it is in her best interests to enter into the transaction, and that this was obvious to the other party (Tyler) and that the other party (Tyler) took unconscionable advantage of the situation. The facts do not suggest that these requirements could be satisfied. There is no suggestion, for example that, because of her age, Tyler failed to ask important questions, or that she agreed to harsh terms, or that she did not understand the nature or extent of her obligations; and that any such thing was obvious to Tyler, and that he took advantage of these circumstances.
See Commercial Bank of Australia Ltd v Amadio.
It should be noted that, even though Sunny has reached the age of majority, this does not in itself mean that the contract could not be set aside on grounds of unconscionable dealing, provided that, in addition to her relative youthfulness and inexperience, the other factors mentioned above could be established.