I love 5th graders - they are on the cusp of adolescence without (yet) all the peer attraction and opposite sex attraction. I taught them for years early in my career and look back on those days very fondly.
As for advice, I would say to a fifth grader: "Explore the world and find your passion. Let's hike in the woods (on the beach, around the lake, etc.) and find out what is interesting there. Read good books (esp good science fiction). Don't over-indulge in screen time. Play. Eat your veggies and fruits and avoid soft drinks and processed snacks. Keep a journal to write down your thoughts and experiences. Life is good at your age!"