HID headlight bulbs gradually lose intensity with usage (and their current requirement increases, which does put added wear and tear on the ballasts). It doesn't matter how old they are, it matters how many hours of use they have on them. If the car has low miles, or is not often driven with the headlamps on, then they're probably fine. But if it's got average or more headlamp runtime, yes, you should put in new bulbs. Use quality bulbs from GE, Philips, or Osram-Sylvania, either the standard type (good price on an excellent GE-made bulb
here), or the
Philips Xtreme Vision if you want to maximize your seeing distance without creating new problems.
Make sure your headlamp lenses are in new condition (no fogging/cloud-up) and the lamps are
aimed correctly.