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
Ride two Sporchids simultaneously for 400m
Complete the game 100%
Discover the bull and the sheep
Complete a challenge holding a Critter
Throw 100 seeds whilst gliding
Orbit the entire planet in BALL mode
Complete all challenges
Unlock all Telerouters
Take a Critter to the moon
Plant 10 Champolines on top of each other
Bounce on a Youch 7 times without touching the ground
Blast a Critter 100m
Flower all STARPLANTS
Rescue MOM
Unlock all seeds
Visit all biomes
Collect all crystals