Originally Posted by
IK_biker
What is relevant here is the usual failure modes for CF composite material.
UV exposure is one of the main root causes for CF deterioration, severely harming the epoxy.
If the fork has been in use for 20 years and ridden often, resulting in lots of UV exposure, the smart move is to replace it.
If it instead has been ridden seldom during its lifespan, I see no reason for concern.
Except the fork would have a UV protecting clear coat on it. If the clearcoat is not hazed or cracked all over, there's very little chance of under-lying UV degradation.
Given the fork a good inspection. If it looks good there's no need for concern. Look for cracking around the steerer and at the dropouts in particular.
Carbon has a theoretically infinite fatigue life. Most failures will be due to either manufacturing defects or crashes. At 20 years, if a defect was going to cause issues, it would have happened. Unless you have some reason to suspect impact damage, I don't see a reason to replace it.