I agree with this, but I would expand this to say that doing his for extended periods would cause further degradation of the battery (I.e. further reduce possible battery life), but it won’t cause any damage to the rest of the computer itself if OP is fine with always using it plugged in.
At almost 6-7 years old, the battery is probably almost shot anyways, so I wouldn’t worry too much about using plugged in all the time. If this was a newer computer I’d say don’t because it will ruin the battery life.