After Effects has a maximum frame rate of 99 fps. If AE interpreted your frame rate as 120 and you played back the footage at 120 then you would have normal speed footage. In every case I've encountered in more than 40 years behind a movie camera the only reason to shoot at 120 fps is to get slow motion footage. To  do that you set the playback speed of your footage.

I have a GoPro3 Black and I've shot a bunch of footage at 120 fps. I usually interpret the footage as 29.97 or 23.976 fps and put the footage in a comp that matches this frame rate. That way I get every frame playing back and motion that's much slower than normal. That's the whole reason I shot at 120 in the first place.

I've never opened GoPro footage on a Windows machine but maybe 119 FPS is the maximum frame rate your system is capable of playing back. My Mac reports the GoPro footage as 120fps but on the older Mac it only plays back at about 80 in the QuickTime player. On the newer machine it plays back at 120, but, except for the motion blur, it looks like it was shot at normal speed.

It's also important to realize that the FPS that is reported is nothing but metadata. It's just like location information, camera type, f stop. It has nothing to do with the frames except to give the software an idea of what speed to try and play back the footage. In production, especially in post production using After Effects, the important thing is getting whole frames into the composition so you can work on the pixels in that frame. Mis-matching comp and footage frame rates results in frames in the comp window that are calculated blends of one or more frames and they are usually a bit of a mess.

I hope this helps.