The truth is, the answer is no.
Testosterone does not cause aggression.
There's even scientific research into the matter!See, this is actually one of these myths created to support the division of men and women into submissive and dominant gender roles. It's one of the myths perpetuated to keep women from pursuing highly competitive jobs and to treat women's sports as softer, weaker, less competitive, etcetera.
It's social indoctrination really.
Boys are encouraged to be tough, competitive, rambunctious, etcetera, while girls are restricted, told to be quiet, settle down, play nice, etcetera.
This can mean that when trans-men are allowed to be men that they allow themselves to experience more of the aggression they've held back in the past, because they're now allowed to be aggressive!
What can actually make you more aggressive however is hormonal imbalance and/or hormonal changes that you aren't fully used to yet. That's why steroids can cause aggression, cause they can cause massive hormonal imbalance when some of the testosterone is converted into estrogen.