Do not be discouraged. If MP is really what you are after then put in some more work and re apply. Come back a stronger candidate. Add courses, certificates and make your self more competitive. Maybe there was guys who were older with more life experience, and education. There is a million reasons why they do not select someone. Same can be said on the civilian side of things. I have personally been through 6 processes. 4 processes with the same service. I do not get discouraged. I do more work and return knocking on the door. After post secondary plus dozen of certificates and courses, plus 3 years of 1st responder volunteering, plus work related experience I don't get why I cant break through... but don't ever be discouraged. Work that little bit harder and return a stronger candidate.
Every time I get the thanks but no thanks email ya it sucks... but you don't give up. They never tell me why I wasn't successful. Just come to terms with the fact that you probably will not find out why they did not select you. You can only use this experience having now gone to a MPAC and build on it when you enter other processes. The MPAC is a very stressful assessment. Probably more so than a civilian process. So now that you have experienced it you should be able to build on it for when you either go back or go some where else.
For me my paperwork did not get processed in time to go to the August MPAC. Now that the paperwork is completed I am hoping to go to the fall assessment. I can use the multitude of interviews I have been through to my advantage so in the future use your experience from that assessment experience to build off of. All the best