Answer:
Probably not, because the terms are not definite.
Explanation:
A contract is considered to be valid when there is a written or expressed agreement for one party to deliver goods or services to another.
The terms are clearly stated. For example the price, time of sale, acceptance of price, and so on.
A valid contract has the following elements: offer, acceptance, agreement, and consideration.
In the given scenario where Kelly tells Matthew that she will sell him one of her motorcycles at some time in the future and Matthew eagerly accepts. There is an agreement but there is no specific offer and consideration of price and also the time of transaction.
So the contract is probably not valid because terms are not clearly defined.