Avatars could be worn by "Newbie" accounts back then, but they were disabled for security reasons in 2013^[1]. Following that, it was re-enabled in 2015, with "Full Members" as a pre-requisite^[2]. And I'm guessing there won't be any additional membership fees to wear an avatar because that's why the forum was hacked in the first place.

[1] Forum avatar?
[2] Avatars re-enabled