Imperial_Samura
Anticrust Smurf
I think whats being said is not that Dumbledore WAS a horcrux, rather that he has one - so Voldermort could fight him, but if he killed Dumbledore then Dumbledore wouldn't really be dead (rather I guess he would be in the state Voldermort was before his resurrection.) One assumes no one would know this (who would think a great and good wizard would have such a dark secret?)
And Dumbledore does know about them, he just needed Slughorn's memory to confirm his suspicions and reveal Tom Riddle's intentions (the seven horcrux theory.) And he is old, probably battled and killed dark wizards at some point, so I guess there's a chance.
Still, I don't think he would have made one. It doesn't seem like something Dumbledore would do, after all, he has the whole thing about not being scared of death, about there being worse things then death (though that could refer to the horcrux unlife I guess) and it doesn't really fit in narratively, if it turns out Dumbledore is alive thanks to dark and evil magic utilised by people like Voldermort, well it's just not in character. Of course it could be asked why he is so against them if he hasn't one and seen what it's like, well I think if he fought and defeated at least one powerful dark wizard (Grindelwald in 1945) he may have seen them in action, perhaps Grindelwald had a horcrux? Perhaps Gridelwald was a Nazi, though that's beside the point, although it would be nice to think Dumbledore fought against the Nazis. That'll teach 'em.
And beside, doesn't the splitting of the soul have effects on the person, both physical and mental? Granted he wouldn't have done it enough to end up looking like Voldermort, but in terms of personality and physical appearance it just doesn't look likely.
As to Dumbledore's age, I too have heard it put at 150 or more, but then perhaps we can deduce it. We know he was around in 1945, and probably had finished school and was powerful enough to defeat a dark wizard (which warranted being recorded on the frog card, so a powerful dark wizard), I'm thinking at least 19 or 20 years of age, most likely a lot more. Likewise, he worked with Nicolas Flamel, who was 665 thanks to the philosophers stone, how long did he work with Flamel? Probably not for 600 years, but a few, he was called his partner after all, and there are no indications he worked with him while he was headmaster, or maybe even as teacher at Hogwarts, so prior to working there (how long has Dumbledore been at Hogwarts?.)