This is the tooth of a 15-year-old boy.
It's his first molar tooth, erupted at age 6.
He has drunk a lot of carbonated drinks, and the central yellow colour on the tooth picture is the dentine, the soft, sensitive part of the tooth.
The white enamel at the side is present as it hasn't had the chewing wear on eating. He has lost all the 2mm biting surface enamel in a tooth that should last another 70 yrs.
It's unlikely to remain beyond the age of 20.
Look at the video on fizzy drinks, and the cost of implants in the adult section.
If children drink any fizzy drinks, less damage occurs if they are drunk cold with ice, through a straw, and only at meal times. No "sports" drink make you perform better. They merely dissolve your teeth.