I can't help with the religion aspect, as that's not a problem in my house, but I can help with the wanting to grow up too fast aspect.
What worked with my DD was extended discussions of how being an adult comes with a lot of freedoms, but a whole lot of responsibilities that end up impacting those freedoms. So, if she's saying we get to go wherever we want because we can drive, I explain how that means we have to pay for the car and insurance, learn the laws, keep up with maintenance, etc, and it's all a lot of work and worry.
My DD got it into her head that adults get to do whatever they want, that they don't have to obey any rules. That led to conversations about the law, law enforcement, the court system, and prison. DD became FASCINATED by the concept of prison, and I have to admit it felt pretty strange to have a 4yo sitting on my lap at the computer, insisting on seeing more images of prison cells, and descriptions of what we're seeing. But it did serve a purpose relative to this conversation, which is that she learned that the consequences of breaking the rules as an adult can be far more severe than anything she's ever experienced.
And on the flip side, there's emphasis on the things she can do as a kid that I can't. Now, I'm not one to pass on jumping on the bouncer just because someone might think I look silly (what's wrong with silly?), but I will pass on jumping on the bed, because I'll break it.
