Alright then, I've been mulling over how best to balance being an older vamp and I think I've come to something agreeable. 

The Long Death: As to make even a temporary death as jarring as possible we will be relying on the whole 'life flashes before your eyes" trope so far as these brief departures are concerned. While being older means you've had more time to accrue primacies it will also ensure you've a longer return trip to be making, should fate be unkind.

A newly blooded vamp of one hundred years or less gives just enough time to say six Mississippis before they re-raise. In lieu of the carefully honed skills and hard won knowledge of their elder peers it is this relentless pace they substitute which makes them a danger. Capitalizing on the six second span of vulnerability each death offers can prove a daunting task, especially when encountered en masse.

The older one gets the longer these periods grow, but never by overmuch. (I'm aware how little one would enjoy roleplaying as a mute/deaf/motionless dead guy/gal for extended periods of time) Instead they will carry the penalty of growing deeper and more troubling. If you poke a few holes in a vamp that's just come into his own he takes a dirt nap, do the same to him in a few hundred years and it's closer to REM. A surviving proverb sums it up nicely.

"The young remember. The old relive. We ancients remorse."

The older one gets the deeper they go and the more disorienting it is to be thrust  back to life. Affectionately known as wraithburn this lasting sickness disorients the re-risen vamp, leaving him weakened and unable to summon his crafts. These fleeting sojourns down memory lane will be your only opportunities to fit flashbacks into the story, so long as they're brief and the transition back to life is jarring. (Imagine reliving your wedding night as a sensation of dreadful self-awareness fills you. In a terrible instant you find yourself no longer twined around your lover, clothes heavy with your own blood. Or holding your infant son only for his weight to be replaced with that of some thrashing monster.)

Here's the rule of thumb:

At 100 years or less you're down for six Mississippis and shake off the wraithburn in a minute, give or take.

More or less every hundred years (Read: Every Primacy you choose) adds the previous count to downtime but tacks another zero on your wraithburn. Here's a handy chart.

100 years or less: 6 Mississippi and 1 minute of wraithburn
100+ to 200: 12 Mississippi and 10 minutes of wraithburn
200+ to 300: 24 Mississippi and 100 minutes of wraithburn (1.6 hours)
300+ to 400: 48 Mississippi and 1000 minutes of wraithburn (16 hours)
400+ to 500: 96 Mississippi and 10000 minutes of wraithburn (160 hours or 6.66 days)

Five centuries is the upper limit on how old you'll be able to make your characters, meaning the were born during the later half of the 1500's.

You'll also notice from the above that potions are more useful as a leg up for younger vamps than they are for older ones (Since they kill you) At 500 years and up a vamp's going to need a damn good reason to quaff one. That said [u]they are powerfully addictive[/u] and those that rely on them as a crutch soon find eternity has a way of catching up to you.