The planet (or ex-planet) Pluto is believed to be about 4.5 billion years old. We have recently learned a lot more about Pluto as a result of the New Horizons mission.
New Horizons has discovered a region of cold, dense ionized gas tens of thousands of miles beyond Pluto — the planet’s atmosphere being stripped away by the solar wind and lost to space. Beginning an hour and half after closest approach, the Solar Wind Around Pluto (SWAP) instrument observed a cavity in the solar wind — the outflow of electrically charged particles from the Sun — between 48,000 miles (77,000 km) and 68,000 miles (109,000 km) downstream of Pluto. SWAP data revealed this cavity to be populated with nitrogen ions forming a “plasma tail” of undetermined structure and length extending behind the planet.
One thing we have discovered is that Pluto’s atmosphere is being stripped away from it. If this process had been going on for billions of years how likely is it that Pluto would still have any atmosphere left? This is evidence that Pluto and the rest of the solar system are much younger that is generally believed.