"Conservative" literally means "no change"; to conserve. Young people tend to be more open to change. When those overlap, you get "inconsistency" as you phrase it. Older liberals are already susceptible to change via attitude instead of age, reducing the potential for an age/openness mismatch.
People don't typically spontaneously change their beliefs for no reason, without exposure to a new idea. Therefore, we can think of belief change as the illness caused by a virus loaded with new ideas that some are more susceptible to than others, by factors of exposure (socialization) and resistance (hardiness against new ideas; conservatism). Young people have a lot more involuntary social interaction from work, school, parties, and combined housing situations (roommates). The only one of those risk factors hitting older married people is work, resulting in less exposure to the new and competing ideas that drive change in beliefs.
While young conservatives might have a greater resistance to the "virus" taking hold from their political attitude, they can still be overwhelmed by the broad exposure they face, whereas older conservative's resistance to change, combined with lower exposure, tends to protect them, and changes in their political views are less common as a result.
Liberals and some young conservatives "catch it", while older conservatives don't, resulting in a mis-match by age among conservatives.
The whole process is called political socialization if you want to dig in even deeper.