Jesse got turned by Darla, same as Angel did, and he fared no better than someone sired by vampire mook#3, so who makes a vamp doesn’t seem to be it (or at least not all of it).
Also, Darla after being re-turned on Angel didn’t come off as anything but what she’d been before (at least until she got knocked up) so age doesn’t really seem to account for much. Hundreds of years vs brand new, Darla was Darla.
People mention what a failure Spike was as human, saying that discounts who you are being what makes a superior vamp, but there’s a lot about Spike that’s fairly unique compared to other vamps. I mean, he actually likes eating human food. Angel won’t even eat donuts, but here’s Spike raving about the onion blossoms at the Bronze. Spike is clearly not the one you base any sort of vampiric theories on, even before getting chipped and souled.
Spike had been a deeply passionate human being, who was being held back by his fears, shyness and social inhibitions. Once his vampirism cured him of these, he was able to redirect his passion to other things, like violence.
It didn’t change completely - look how sappy and romantic he got over Buffy. Or even Drusilla, for that matter. You see a complete reversion to type when Dru starts to get with Angelus again, and Spike is powerless.
I don’t think his personality changed all that much. His love for Drusilla was just as obsessive and stalkery as his love for whatshername he wrote poetry about. And, of course, his love for Buffy took obsessive and stalkery to whole new levels! Yes, he found himself a set of cojones, but his underlying persona remains the same.
ETA: Or, er, what **Steophan **said.
He was certainly not established as a vampire. He was described by Giles as a demon who drew power from an amulet. His biggest enemy was the mayor, who was certainly NOT a vampire, and defeated him by doing…something…with the amulet a few hundred years before. The big morbidly obese demon monster had a bunch of vampire minions, but I don’t think he was a vampire himself. He was killed with an electric shock in his bath tub, which as far as I know is non-fatal to vampires.
I wasn’t personally responsible for winning two world wars and one world cup against the Germans to respect their linguistic sensibilities, thank you very much.
