To determine the type of data presented on the y-axis, I would need to see the scatter plot diagram, which you mentioned. However, based on the typical context of scatter plots, if the x-axis represents "age," the y-axis could either represent "credit card debt" or some other variable related to age.
If your scatter plot is comparing age to credit card debt, it is most likely that "credit card debt" is presented on the y-axis. Therefore, if the x-axis is "age," the type of data presented on the y-axis is likely "credit card debt."
If you specify what is shown on the x-axis, I can give you a more precise answer!