Time Poem by Paul Perkins

Although for me there's seldom haste,
I could not, if I wanted, stop.
The elders, I leave in a chase,
and children let me go to waste;

Invisible! That's what I am,
and yet, I'm seen on things of old.
I kill, I heal, I fly, I creep...
I'm even moving while you sleep;

Polite take me to say, "Yes Maam";
I'm even used to smoke a ham.
My mark is formed within in a tree;
Now try to guess what I may be.