Ellie's world is changing: her mother keeps hoping Ellie will find her passion in theater; her bff is spending most of her time with new volleyball friends; her grandfather has moved into their house. That last one is really weird, because her grandfather is now a middle-schooler, after his scientific discoveries on reversing aging. As Ellie gets to know her grandfather as a peer, she also gets to know herself, and finds her passion in science and curiosity. 
 Sci-fi-ish, but in a subtle way-- more requiring a suspension of disbelief than an interest in science. This is more about growing into self-discovery than action-adventure, and would be a good choice for the sixth-grade reading list.