I'm helping my girlfriend in her schoolwork and she is trying to propose an app that would allow people to make small personal loans in a responsible way (with simulations, etc...) She needs to quantify what is the target market sector, it's size and potential, etc...

I told her I would try to help her find data but I don't know where to start. I was thinking maybe a data set that would show people's saving per age group and stuff like that would be helpful. Does anyone know of a respected data set that she could use? She is a student at University so can be behind a paywall, and European data would be nicer but anything would be ok. I can only seem to find retirement ads or data for euro countries without splitting the age groups.

Thank you so much in advance for any input.