Member+ requirements: there are no hard requirements. It's just a sense of being active on the forums and generally knowledgeable. You can apply yourself, be nominated by someone else, or be promoted by an admin.
Member+ bonuses: Access to the Exclusive Board, which contains within it the voting boards for Member+, moderator, and Distinguished Member. Pretty much everything above a regular member has this level of access, though. Nothing really exciting goes on in there these days, to be honest.
Oldbie requirements: You had to have been a member of a predecessor of Glitch City Laboratories forums before the opening date of said forums, which is December 2005. The age of the GCLF account itself doesn't factor into this at all, as the only requirement depends on forums older than GCLF began. Previously the requirement was to be a member of the very first forum, Professor Glitch's Laboratory forums, prior to that forum's closure of November 2004. Because most of these forums are no longer online, it's not possible to verify these requirements, so you just have to trust me when I say someone qualifies for oldbie status.