IF: What is the average age of an MSCA fellow and do I stand a chance with applying when I am above or below the average age?

The Individual Fellowships do not have any age restriction. The average age of fellows in FP7 - the predecessor of Horizon2020 - was 34.7 years. (The statististics for Horizon2020 are not yet known.) This does not mean that you do not have chances for applying when you are older or younger than this. Evaluators typically have a look at the CV and put it into context. A researcher should well justify any career breaks. Keep in mind that any applicant has to show the impact the fellowship will have on his or her future career path and adapt this to your individual situation. 

The results from FP7 showed REA and the EC that for Individual Fellowships (IEF, IIF, IOF and CIG, now all combined under the EF and the GF) there were indeed many successful applicants from the age of 50+ compared with how many applications were received from this category of researchers.