The Growth Journey (Steam key).

http://store.steampowered.com/app/416610/The_Growth_Journey/
A game about permanent growth. Once you grow, you cannot shrink.

Hitting something means death.

There are blue colored zones, (grow zones) each letting you grow a fixed number of times (displayed inside the zone) by a certain percentage.

And then there are green colored zones, (gates) which will only let you through if you are of a certain size. (displayed inside the gate)

So growing up has its advantages and disadvantages.