I would not prune it yet. I would wait this year. Mine took years to bloom. I also love the leaves, and I love how tough this plant is. However if it is too big for the site you might want to move it.
I have a thread on the "other" website about a hybrid own-root tree peony I have that was knocked flat in a windstorm. It grew up like a palm tree that year and was bizarre. So the next spring I whacked it off to near the ground, just as the buds were swelling. I cut just above the loest buds. It grew beautifully that year, all bushy and nice(over 4 feet tall) and it even bloomed the same year. I am considering doing that to my P. lutea this year, as it is a bit scraggly. I learned from the other experience that these are hardy shrubs and respond to severe pruning just fine.
p.s. I have a tree peony 'Tria' which is a soft yellow (my P. lutea is bright brassy yellow). If you like I could try to layer you a start, some of the branches are touching the ground already.
