My oldest villager is Bruce, he's been with me since 2013! It's so weird to think about how he's been there for 3 years y'know? I love him though! He always visits my house and gives me fruits and such.
Pierce is my last starter to stay in my town. And he always will be, because I refuse to let him leave. The first one to actually move into my town was Curlos! He's staying also.
My oldest (and my most favorite) villager I still have currently would have to be Fang. I recently got access to an old photobucket account and found a picture of us together in city folk. c: He was one of my originals so I've had him since 2009. I played AC:GC as well but my town was reset so I believe Fang is still the oldest.
Since I don't have access to my GC game, my oldest villager in my NL town is Lolly. I moved her into my new town, not really new anymore, 2 days after it was created. She was my first move in, but unfortunately due to missing some play time a while back, I lost all of my starter villagers over time. I could always get them back now, but it bugs me when I see the move in date on my town tree. I like it when you can't see it...
Grizzly, Peck, Merry and Aurora were my starting villagers. I bought New Leaf when it was first released and I still have them. Rodeo was also a starter, but he moved out because I didn't know how the villager move outs worked.
Marshal. I couldn't actually remember so I had to take a look at the town tree, apparently it's marshal them fauna and then fang.
I had all three of them pretty close together, that was only about 7 months ago though so I haven't had them as long as some people have had their villagers for. But im pretty sure they're all going to be very permanent villagers