Play a Killoren. They only get to Old age, then they stop aging.
Also, Druid 15 (obviously) makes you stop aging, but you still die. Tattooed Monk can do the same.
Cloud Anchorite (FrB) works differently. You still age to old age, but you never die. Combine that with Tattooed Monk and you could be young (ie - no age penalties) and then hit Cloud Anchorite 10, and you'll never die from age. You'll be immortal.