Peonies do not grow old and stop blooming. Voles could be damaging the roots so if you see tunnels or caved in soil that could be the problem. Another thought is that mulch or soil has been pushed on top of the peony roots and they hate being planted too deep. Try scraping the soil away from the top of the plants so the roots are just barely covered with soil. Prune the plants to the ground in October and see what pops up in the spring. If voles damaged the roots a year of new growth means you might have a blooming surprise next spring. Keep growing, Marianne Binetti