The first aspect is simply that you are still very young, so many things can't be solved, just the problem of age and experience, which will get better and better with the accumulation of years.

The second aspect is that you are still too naive and immature to take responsibility. In fact, this is also a polite refusal, because your state is not enough to give a girl more sense of security, so she will gently tell you that it is not your problem, but that you are too young.