Hey! I am no professional, but this idea occurred to me- maybe to address the maturity issue- you can try to use a really limited colour palette, maybe even one colour. For me- colour palette like that in a peace make me feel more serious towards it. You know also maybe thinking about how colours can make us feel. Again, I am really new to art so I am no expert, but just as a viewer- those are the things that are important to me visually. Hope this makes sense:) have a good day <3