Like Autumn, growing up is bittersweet.  Poet Billy Collins says it well.

On Turning Ten

The whole idea of it makes me feel
like I’m coming down with something,
something worse than any stomach ache
or the headaches I get from reading in bad light–
a kind of measles of the spirit,
a mumps of the psyche,
a disfiguring chicken pox of the soul.

You tell me it is too early to be looking back,
but that is because you have forgotten
the perfect simplicity of being one
and the beautiful complexity introduced by two.
But I can lie on my bed and remember every digit.
At four I was an Arabian wizard.
I could make myself invisible
by drinking a glass of milk a certain way.
At seven I was a soldier, at nine a prince.

But now I am mostly at the window
watching the late afternoon light.
Back then it never fell so solemnly
against the side of my tree house,
and my bicycle never leaned against the garage
as it does today,
all the dark blue speed drained out of it.

This is the beginning of sadness, I say to myself,
as I walk through the universe in my sneakers.
It is time to say good-bye to my imaginary friends,
time to turn the first big number.

It seems only yesterday I used to believe
there was nothing under my skin but light.
If you cut me I could shine.
But now when I fall upon the sidewalks of life,
I skin my knees. I bleed.

Billy Collins