Age is the estimated amount of time that an existing bulb has been used. Age, along with the schedule and life are used to estimate when the existing lightbulbs will burn out next.
Generally, an exact number for each light bulb is not available. We suggest interviewing your site contact to determine the best estimate for this field.
In zones where multiple bulbs are used, the average age of the bulbs or the average age of the existing fixtures would both be acceptable inputs for age.