If he are using specific character BP’s for old people, or if those NPC’s are at least created with a specific ID. Could he not just set the max walk speed for them in AI controller with their own anim_BP/blend space for how they transition from idle-walk-run and so on?
The state they get like e.g run/walk will only tell them to switch to another speed and go to walk/run in the anim_bp. The animations can be different, and the speed those chracters have could be set based on what the max speed is given to them. And not through BT parameters?