I'm not an expert so please correct me if I'm wrong, but that looks similar to a P. lutea. It is a species peony that can cross with other peonies to create hybrids or self-fertilize in isolation. P. lutea is a vigorous plant and it does indeed have yellow flowers. That is the largest peony plant I know.
This is an older one at a nearby university garden. It is 7ft x 9ft. Paeonia lutea var. ludlowii:
Flower:
I don't know why yours isn't flowering. It looks like it gets plenty of sun. Have you fertilized it? I often read that adding too much nitrogen will cause it to forego blooms over foliage.
I think it's a beautiful plant, but it certainly needs its space.
