what am I?

Am I a tree?
Strong and sturdy, totally sure
Swaying in the wind, yet not falling down
No I am not a tree

Am I a rock?
Strong and hard
The years slowly eroding me away
No I am not a rock

Am I a river
Flowing upon a set path
My water level rising with each day
No I am not a river

No I am a mystery
I am unsure and unsolved
I am youthful and unknown
Maybe one day I’ll be a rock or a rock or something of the sort