You Need a Head Start, Right?

You can turn on your flashlight at the same moment. As long as he has a physical head start. The distance to that horizon is the speed of light squared divided by your acceleration. So if you're accelerating really, really fast, then that horizon is closer. If he's accelerating really, really slowly, the horizon needs to be further, further away so his acceleration goes to zero. That is infinitely far away. But time equals infinity isn't a real time. The universe could go on forever, we'll never get there.