The lifespans of the nobles of Amber, and those of powerful bloodlines of the Golden Circle, are lengthy. Lifespans do vary by House, as well as individual; closeness to one of the Princes or Princesses is known to extend life. (For instance, Sir Rein, who seems ever young in Corwin's memory, is likely to have an extremely long lifespan.) When creating background and history, consider how quickly the generations pass.
As a rule of thumb, a generation in Amber equates to approximately 100 years. The specifics will, of course, vary wildly but that is the conversational yardstick. Characters are often considered youthful, in a twenty-something sense, for their first two hundred years or so. Maturity tends to cover the next hundred or so, and the period that might alternately be called 'Middle Age' and 'Prime' the next hundred. After that it tends to be very idiosyncratic. Some slip into old age with grace and regularity but some, especially those of great power or presence, can maintain at that state for centuries, to as much as a millennium. Lifespans beyond this are not unheard of, but they are rare enough to merit comment or require some other explanation. This model applies equally well to people of import from the Golden circle, notably those with appropriate blood gifts.
Certain gifts confer longer lifespans or delay the ravages of age. The lifespan of gods (DIV-GD) and princes of Amber (BLD-OB) far exceeds the guidelines above, and the age they appear to be frequently has little bearing upon their actual age. Those of the blood of House Mandrake (BLD-MA) can expect to live fully half again as long as their counterparts. Other characters with exceptional lifespans are required to both justify it in their concept, and buy it as the long-lived gift (PHY-LL). Greater lifespan does not mean that a character necessarily remains youthful; those blessed with youthful vigor (PHY-YF) age more gracefully.
Regardless of gifts or backgrounds, we do not allow characters born before the rule of Faiella, and all memories of the time before her reign are hazy at best. (Benedict is the sole exception, and even he does not clearly remember that early time.)
We have no minimum age for characters (meaning that you can, if you choose, play a child), but we reserve the right to limit the gifts permitted to children (i.e., they cannot survive walking the Pattern, and so forth). We do not have extreme fast-time shadows, and game time moves at a rate equal to real time, so keep in mind that children will age slowly.