Why is Big Mac still at CHS?

[joshuachasseur 6]

This is a small nitpick I noticed, but if AJ is supposed to be a senior,then why is Big Mac still at CHS seeing as he's her older brother?

[Will Guide 21,325]

As far as I can tell, his appearances at the school in the first film were because he's volunteering and not an actual student. You don't have to specifically be a student to work there!

[azbat 301]

Big Mac  "I get older, the fillies stay the same age."