Explanation:

- Interest in favor of an unborn person is typically created through a trust or a will, intending to benefit them once they are born.

- Up to Minority: This option suggests that the interest lasts until the beneficiary reaches the age of majority, which is the correct interpretation.

- Youth: This is a vague term and does not define a specific period.

- Major: This usually refers to someone who has reached the age of majority.

- Old age: This does not relate to the creation of interests for unborn individuals.

Given the context, the correct answer is:

- Option 3: Up to Minority