I'm 43. I have a knee replacement and now problems with my shoulder. Strong osteoarthritis. Also ra. It is normal at my age?

No it is not. Most people, at 43, do not have osteoarthritis - a wear and tear condition. Rheumatoid arthritis, however, is a condition where the body attacks its own joints leading to damage. This should be followed by a rheumatologist carefully. Most osteoarthritis appears later in one's 60's and 70's.
See details. If your RA is uncontrolled, early and significant joint damage can occur. Are you under the care of a rheumatologist? Also, previous trauma to a joint may cause earlier and more significant osteoarthritic changes.