Here is the full list of all 18 Grow Up achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Discover letter block P
Discover the bull and the sheep
Ride two Sporchids simultaneously for 400m
Collect all crystals
Complete the game 100%
Take a Critter to the moon
Blast a Critter 100m
Complete all challenges
Throw 100 seeds whilst gliding
Plant 10 Champolines on top of each other
Unlock all Telerouters
Unlock all seeds
Orbit the entire planet in BALL mode
Rescue MOM
Flower all STARPLANTS
Complete a challenge holding a Critter
Bounce on a Youch 7 times without touching the ground
Visit all biomes