A more thorough explanation:

Ancient, adj. refers to something that has existed for a long time without interruption, usually for at least 20 to 30 years. For example, an ancient deed or an ancient map. Even if proof of validity cannot be made, ancient items are usually presumed to be valid.

Ancient, n. can also refer to a senior member of an Inn of Court or of Chancery.

An ancient castle in Scotland has been standing for over 500 years.

The ancient manuscript was discovered in a cave and is believed to be over 2000 years old.

In the legal world, an ancient deed can be used as evidence in court even if there is no proof of its validity.

John is an ancient member of the Inn of Court, having been a member for over 30 years.

The examples illustrate the definition of "ancient" as something that has existed for a long time without interruption. The ancient castle and manuscript have been standing for centuries, while the ancient deed has been in existence for at least 20 to 30 years. The legal example shows that even if there is no proof of validity, ancient items are usually presumed to be valid. The example of John being an ancient member of the Inn of Court shows that "ancient" can also refer to a senior member of a group or organization.