Thank you for the detailed answer. If I understand correctly, it is not possible to test directly the main effect of group with repeated measures 2x2 design. As such, I have another question. What is the approach to test the main effect of group with two groups, two sessions while accounting for the age variability? Does one have to construct a separate design? These questions might be straightforward, however, some explanation would be helpful.

Thank you again for helping with the design and NBS.

Best regards,
Maksym