Is it possible to take someone else’s name who has been inactive for 18 years?

It's not possible if its being used by someone else.

Darn. I assume there is no expiration date for accounts correct?

Accounts do not expire.

They should, most likely that person's never coming back.. if it's been 10 I think they should expire the name and have it automatically changed to like member#1, #2, #3, and so on, and same thing goes for banned members, or people with scam / locked tags, if they are inactive with a scammer lock tag then 10 years if they are banned then it should be instant.

Just a thought.

I concur

Old and inactive user accounts will not be renamed/deleted under any circumstances.

For your reference: https://forums.d2jsp.org/info.php?p=3