It's been available on Steam since Midnight this morning. HOWEVER
I'm definitely holding off on buying this based on the hijinx going on with the patch update. Thankfully disabled that so my game is untouched. For me, the patch issue isn't Sims aging up, but incest/inappropriate relationships sims now have.
And from past experience, it's also likely this disturbing bug will be a challenge to fix by EA. It's one thing if your family sims are attempting to have inappropriate/romatic relationships with other family members and/or strangers (like adults trying to date child sims etc.). At least you can address and fix that.
But with Neighborhood stories, this problem becomes pandemic with townie sims being randomly pushed into such relationships. And since these new interactions are necessary to support HSY EP, there's a good chance EA will do the minimal effort necessary to address this. Then move on to other things.....