The gripping tightly is a sign of insecurity (ie you're not a good perch and he feels like he is going to fall) and the 'aggression' is going to be hunger. I would start feeding him something around 100 grams (and weigh it, don't just guess) and see if he calms down after that. Weigh him, and his prey items. This time of the year, and at his age, he's no doubt trying to get ready for the breeding season (whether or not you have females) and they try to pack in all the food they can. My 'small' is a rat that's going to be 40-60 grams, which would be fine for an off-season male, but I would try getting him what I consider a 'medium', which is going to be a rat 100-150 grams and see what he thinks about that.