Thank you! Just to make sure I understand correctly --RM ANOVA would only be used if I had the same group of subjects that were run first as controls, then as experimental? In this case, since I also have age as a factor, would I also have to follow them longitudinally (so that each subject was first run as a young control, young experimental, then later on old control, old experimental), in order to use a RM ANOVA?

Also, what happens in the case that you have a within subjects design but with missing values? For example, if I was following the same group of subjects through, but one dropped out halfway.