The fridge, roof AC, converter/charger, house and starting batteries, fresh water pump and awning fabric on our rig, bought new in 2003, lasted around ten years. Health issues etc., curtailed use and mileage is only about 10,000.
Engine/drive train is fine. Tires are safe for about 5 years may then become unsafe due to sidewall cracks just from sitting parked. Water damage can be very expensive to repair. Rigs in sunny dry climates will often be in better condition overall except for fading graphics and exterior finishes. Consider all costs including probable major repairs and replacements including tires every five years when deciding on buying a used vs new rig. Paying an RV service and pro truck mechanic to inspect a used rig and give you a written estimate for repairs/replacements may cost you over $100 but could be well worth it. Don't buy on impulse, make sure that the length, floor plan storage space and sleeping arrangements will be OK for you and yours.