I also could not stand until I had been riding 3-4 years. And I still can't get myself up on a very steep climb, which is why I spin up. I lose so much power if I stand, I am not sure it's worth it. I do stand sometimes on shorter, easier climbs, to change position and rest my back. I guess I am just weak, despite all of the stuff I do!
Catrin, I know what you mean about the trainer. I find it feels very weird and almost unsafe. I have to put it in such a hard gear to avoid that feeling that my cadence plummets.