Depends on your skills and time available, or if will you be paying someone.
If paying someone and they show no sign of current problems, then wait till they do show a problem.
If taking the hubs apart and cleaning them is no big deal to you, then sure that makes sense. If it's something you aren't sure of your capabilities, then maybe wait until a problem shows. Since this bike is for another, if you are not competent and confident of your skills at adjusting bearings, then you might be endangering the one you are wanting to keep safe. They won't necessarily realize when a wheel is going wonky as they ride.
As for the BB, if it's a cartride BB, why change it if it's not showing problems? If it's cup and spindle then the same recommendation as for the hubs.