Aggression doesn't matter, I think. I got a player with 7 yellow cards this season, who has his lowest % at aggression: 88% (overall % are 132%). My highest aggression guy is 163% (overall 128%), got no card at all.
I also have a 98% aggression-guy, who recieved only 1 yellow card and a 143%, who recieved 5 cards...

I think it's only this season, because I collect all (important) data after the season is over:
This season, my squad revieced 33 cards in only 38 games, last season I played all 52 games (won triple) and my squad recieved only 21 cards. The squad is nearly the same (only a new AML is in the squad).
The season before were also all 52 games played, recieved only 23 cards.