Yup... tomboy is a time-bound statement from gendered societal expectations.

I was a tomboy, my daughter did the same kind've stuff I did, was was just another girl... Its one positive improvement in society over the past 30 years.

If you get a chance, listen to the song "When I was a Boy" by Dar Williams.
It gives a great explaination/feeling of tom-boyish-ness and society's expectations for girls - and also for boys... She's explaining what she could do when she was a 'boy', but how now she is a grown woman, society constrains her behaviour. Very clever and a very pretty, easy tune to listen to.
Lyrics below.

I won’t forget when Peter Pan came to my house, took my hand.
I said I was a boy, I’m glad he didn’t check.
I learned to fly. I learned to fight. I lived a whole life in one night.
We saved each other’s lives out on the pirate deck.
And I remember that night when I’m leaving a late night with some friends
And I hear somebody tell me it’s not safe, someone should help me.
I need to find a nice man to walk me home.
When I was a boy, I scared the pants off of my mom
Climbed what I could climb up on
And I don’t know how I survived, I guess I knew the tricks that all boys knew
And you can walk me home, but I was a boy too.

I was a kid that you would like, just a small boy on her bike
Riding topless, yeah, I never cared who saw.
My neighbour came outside to say, “Get your shirt,” I said “No way,
it’s the last time I’m not breaking any law.”
And now I’m in a clothing store, and the signs say Less is More
More that’s tight means more to see, more for them, not more for me
That can’t help me climb a tree in ten seconds flat.
When I was a boy, see that picture? That was me.
Grass-stained shirt and dusty knees.
And I know things have gotta change, they got pills to sell, they’ve got implants to put in, they’ve got implants to remove
But I am not forgetting
That I was a boy too.

And like the woods where I would creep, it’s a secret I would keep
Except when I’m tired, except when I’m being caught off guard.
I’ve had a lonesome awful day, the conversation finds it way
To catching fireflies out in the backyard.
And I tell the man I’m with about the other life I’ve lived
And I say now you’re top gun, I have lost and you have won
And he says, “ Oh no, oh no, can’t you see
when I was a girl, my mom and I, we always talked
I picked flowers everywhere that I walked.
And I could cry all the time, now even when I’m alone I seldom do
And I have lost some kindness,
But I was a girl too.
And you were just like me, and I was just like you.”