If it is an old house then graying lumber is not such an extraordinary thing. Poke the ceiling joists with a sharp object (like a skewer) and see if you get easy penetration, if you do then most probably a repair job is in order.
Plaster being loose from ceilings in older homes again is a common occurrence, sometimes it is very localized and can be fixed reasonably easy, other times it's well spread and usually removal and replacement with drywall is the best option. ( NOTE: this is a MESSY option.... ).
Without further description from you (or pictures) it's hard to give any other advice.