A timeline for the basic events would be nice. In Future Trunks canon he looks like he would have been 19 when he killed the Androids? I kinda wanted her to be like 5 when Gohan died, but it looks like if she was 12 she'd have been 17 when Future Trunks orginally kills the
Androids.
The timeline we are working with for this game is as follows:
Trunks is born Age 766. Goku dies of Heart attack virus the same year. Dr Gero without the focus of "Kill Son Goku" invests more in programming 17-18 for World Domination, this doesn't
fully take but gives them a mental framework more sociopathic than the altered timeline versions of main timeline Dragon Ball.
Age 767 This is when 17-18 are activated. They kill Gero and begin their reign of terror on Earth, killing off the remaining Z-Fighters. Eventually leaving Gohan as the last traumatized survivor.
768- 779 The Twins run wild on Earth, killing cities worth of people for fun and using Gohan when he eventually trains himself up to Super Saiyan as their personal punching bag.
In Age 780. Trunks goes SSJ at 14, after Gohan dies. In this timeline Gohan's dying words were a taunt towards 17-18 that once they killed off everyone on Earth they'd have nothing. They actually listened to this, stuck around Gohan's corpse, laughed at Trunks going Super Saiyan and after thrashing the poor kid they dragged him back to Capsule Corp with a "Build us a spaceship or the brat gets it" threat to motivate Bulma. Later in that year Bulma completes the spaceship and they are off to make problems on the interstellar stage.
780 - 784 Trunks spends two years training SSJ while helping efforts to rebuild the Earth, then begins training others for two years.
The Game starts in Age 784.