It seems that advanced incarnated souls would warrant an advanced higher self. Is that the case? And do younger and much less mature soul incarnations have a less advanced higher self managing that role for them?

While this is literally correct, it is not particularly a problem that is insurmountable. There are old souls and there are young souls, the latter being more newly created, but that is in a relative sense—they were not born yesterday, so to speak. They are privy to and witnesses to much of the history behind your current situation and have existed as long as humanity itself, it is just that they have less of a background with the precursor events within the universe and other universes as a kind of deepening and seasoning. But it is certainly the case that a soul extension incarnated as a physical human will enjoy the benefits of accumulated wisdom of its own soul as a resource, and so there is a contrast and differentiation between the old and the new with regard to the depth of awareness, knowledge, and capability, primarily from the broader perspective of more fully appreciating all that can happen as a consequence of the efforts underway. The best analogy we can give you is that a human community in a time of war calls upon each individual to cope in some way or another that is new to them, but much more so to the young than to the "old hands" who have perhaps lived through other wars or, by virtue of their greater maturity or wisdom, can better see all the consequences, all the entanglements, and have a better ability to predict how bad things might get and therefore what precautions to take to mount defenses and seek safety in the most effective way, and so on. The young, especially the children, will be quite helpless and confused. The newness of the situation will be not only upsetting but often incapacitating because of their lack of experience to draw on. So they may not even envision the need to escape, let alone have the wherewithal and the savvy in knowing how to reach higher ground to survive. The old souls will always have more to work with in their makeup, so this is not about judgment or worthiness, it is simply a study in levels of completion that are attained through life experience versus the newbie who is still learning the ropes. All are worthy and the newcomers, in effect, have more work to do but, by the same token, they benefit from the many blessings and hard-won lessons learned by their elders. In the same way that the newcomers provide opportunities for mentoring and teaching, that further adds to the character and wisdom of the old souls so, each in their own way, all are winners from this schema.