$60 single rebuy MTT with $25 add-on about 100 runners 

First time playing this 8k guaranteed live MTT. Starting stack is 12k with 25 min levels 9 handed. 

About 45 mins in to the tournament and have a decent feel for the stronger players and fish at my table. 

I pick up KK UTG on 100- 200 blinds and raise to 500 with a total stack of 11k. Folded around to the Small blind and he 3-bets to 2100. He is a 60 year old guy and has already doubled up to have a stack of around 25k. It looks super strong due to his image and appearance. I feel that he has at least QQ. I 4-bet huge to 6k, effectively pot committed with around 4 k behind. He insta 5-bets all-in. I tank knowing an old guy will never act this strong unless he has AA or he is sick. I tank with my KK for about 1 min and of course call.  

He flips AA and it held up. 

I feel like it is hard to get away from, mainly due to the fast structure of the tournament. but I should have kept my 4-bet smaller to around 3500ish, then if I did want to trust my read if he would go all in, it might have been a little easier spot. But I'm not that big of a nit to lay it down. 

Any thoughts or comments would be appreciated. 

Matt