Butler is a Series-3000 mechanoid. Yet, in Out of Time (1993) it's revealed that the series 3000 mechs are perfect human replicas.
Butler offers the Red Dwarf crew champagne. Rimmer takes a glass of champagne but as a hologram, he wouldn't be able to drink. Hardlight holograms are able to eat and drink.
Kryten says he was created 2.9 million years ago but he has been with the crew at least 3 million years.