Mr. Trick was first introduced working for Kakistos. Trick grew tired of his ancient ways and left Kakistos before his death. Trick then organized Slayerfest '98, which caught the attention of The Mayor. Trick was pretty much forced into working for The Mayor, but I don't think he really minded anyway, as they both had the same goal. Trick worked with The Mayor for a number of months, but in the end was killed by Faith when he tried to kill Buffy.
Trick is a very modern Vampire, so I would guess he's not very old. He could be, because he was pretty strong, but I doubt it. He's probably only a few years old, but was just naturally a little stronger then other vampires, for whatever reason.