Absolutely. People develop at different rates and that is certainly something to bear in mind. But you may be interested to know there is another less familiar argument that suggests that our understanding of consent is actually flawed.
I'll come to the precise argument shortly, but I'll first motivate it by listing some frequently performed actions that flagrantly violate the lack of ability to give informed consent. For example, doctors giving medical treatment to young children. Or representing a child's legal rights in court. Less obvious examples might be forcing children to absorb our idea of an education, play sport with a child where that would give rise to risk of injury (maybe teaching children to shoot a gun), or even giving a child a name. Actions like these are big problems for informed consent fundamentalists. Incidentally, a common first response to a list like this is "ah, but medical treatment or legal representation are necessary, that's why they're exceptions!" Unfortunately this is completely wrong, as either of these could be "nice to have" but not strictly necessary. More on this shortly.
So now to the argument itself. It says that when somebody cannot consent to X, it is OK for B to do X if B knows X to be responsible in all the circumstances. In other words, where A lacks the experience to consent to X, it's OK for B to do X if B has the experience to make up for A's inexperience. So for example, even if a child cannot give informed consent to medical treatment, it's OK for a doctor to perform the treatment if they think it would be the responsible action in all the circumstances. That is the case whether the treatment is strictly necessary or merely "nice to have". Or, even if a child cannot consent to a particular education, it is OK to force them into it if giving them that education is considered the responsible course of action (that's why we can send children to school, despite any protestations).
It's important to note here that B retains liability for an irresponsible action! This is fundamentally different to the case in which A can consent, where B is immediately relieved of all liability, no matter whether the action is responsible or irresponsible. For example, if parents opt for prayer instead of western medical treatment for their child, the parents would be liable for harm done to that child. Law courts have in practise convicted parents of murder in cases like this, which suggests that this argument is in fact implicitly applied in practise.
Assuming this argument is correct, we can now see the problem with the common understanding of informed consent : It takes a special case (the adults-only theory) and applies it verbatim to the general case (children). What we really wanted to do was take the general theory, and specialise it for adults!
So how does this all apply to sex? Well, even if a child cannot give informed consent to sex, this theory would infer that it would be OK to have sex with the child if and only if it would be responsible in all the circumstances. This begs the question "what is meant by responsible?" Well, that is of course up for debate, but some factors involved might be
These considerations actually support the general notions that "younger is worse" or "greater age difference is worse". For example, if younger children are less willing to have sex and are more likely to suffer psychological and physical trauma from sex, then the proportion of cases in which it is OK to have sex with a child diminishes with age.
So, we have now reduced the ethical question of "is it OK to have sex with a child?" To "when is it responsible to have sex with a child?" That is a question that can be given a concrete answer by science. The important point to note here is that mere lack of informed consent does not rule out the possibility that sex is OK!