Peter Davison and Matt Smith were both the youngest actor at the time to take on the role of the Doctor.
There’s a youthfulness in the pair of them that sets them apart from any other Doctor.
Watching Peter’s Doctor as I write this, I can see where Matt Smith gets the “old-man-young-eyes” thing from. Ironically, the two youngest Doctors, in my opinion, are the best at being - well, old. It’s not very often I look at either of them and think of them as twentysomethings.
Even the way they confront enemies and aliens is the same. I could quite easily see Matt in “Earthshock” or “Warriors of the Deep” and the same can be said for Peter in Matt’s episodes.
There might be 29 years between the beginning of Peter’s Doctor and the beginning of Matt’s, but they play the exact same character, in the same show.
Imagine Matt Smith in “Earthshock” - leaving the ship that’s on a collision course with Prehistoric Earth, with Rory on board. Amy and River in the TARDIS pleading with him to go back, Matt doing his whole, “Fixed Points/Temporal Tipping points” thing and being unable to do anything about it.
I’m not really sure where I’m going with this, I just kinda wanted to put some thoughts out there.