You get to a point size-wise where eventually you stop just getting bigger, and you start getting denser. This happens when the force of gravity overcomes a force stopping things from compressing. There are many such forces, and thus many such points where "object gets bigger, then starts getting denser, then starts getting bigger again, then denser again, etc" as you add more and more mass.

I thought that was what you were saying. This is something neat to point out to people. Jupiter and Saturn are not that different in size; Saturn is 9.5 earths wide and Jupiter is 11.2 earths wide. If you could find three more Jupiters and dump them into our current gas giant, the resulting planet would be SMALLER than the current one! Jupiter size objects don't really start to get bigger until they start fusing deuterium and become brown/red dwarfs.

Again! Speculation on my part! Take it with a grain of salt! Please don't use concrete language like "is" or else I'll regret posting my thoughts and will take them down so that people don't get confused.

Yea, I'm jumping the gun here. Here is why I said that with certainty, and thank you for making me defend such a definitive statement. We have six "young" surfaces in the explored solar system. Venus, which looks like the whole planet resurfaces itself every few million years, which along with raining METAL and having a surface that can melt lead just adds to the weirdness factor. You have the Earth which resurfaces itself due to tectonic plates moving, water erosion, wind and biology. The impact that finished off the dinosaurs is 200 miles wide, yet was not discovered until the 1980's due to it being eroded away at the surface. Then you have Io and Europa. Io was until this month the youngest surface in the solar system. Io is also the most volcanic body in the solar system. Europa has resurfaced itself "recently" as in the last few 100 million years. Enceladus has a young surface where the geysers are spewing water ice back onto the surface of the moon, and Titan has active weather that is at least masking the age of the surface.

All of these ages are mostly determined by crater counts.

To not see any craters on Pluto was a shock to me. I was expecting a mix of Triton with its ice geysers and Ceres with its heavily craters surface. The "easy" answer is that there is a mechanic like we have already seen in the solar system reworking the surface. I hope that the real answer is something more odd and interesting!