Smooth skin of youth transitioning into the stringy red-brown bark we know and love.
Bark will thicken a bit more over time, retaining a fine, striated appearance well into old age.
I forgot about this thread thanks for bumping it @Cruiser.
Mt. Tabor Oak that I got last year and it has been a rehab project. The trunk was covered in moss and sloughing off after I cleaned it it but it's bouncing back.