They are no longer a real part of time, and thus can become stuck in the time frame in which they were embraced. This can even lead to some Kindred destroying themselves, or at least going into self imposed Torpor or seclusion. I suggest giving most of your Elder vampire NPC s traits from the time period in which they were embraced. Vampires are dead people that drink blood to survive. They no longer follow the same laws of nature or science as humans.
Vampires are only creatures acting like humans.
Once again, as Storyteller, you can stress this through NPC s. Have humans remark about how pale the player characters skin is, or how strange to the touch. Make a shop owner note how the characters eyes are a strange color, or oddly hypnotizing. Make a dancer in a nightclub remark that the character needs more sun. Always remember that the vampires are only pretending to be human.