Little finger problem (Gathiya/Artritis)

I am 70 years old and experiencing a problem with my little finger, commonly referred to as "Gathiya" (arthritis) in Hindi.  My little finger has become stiff, painful and appears to have an abnormal bend or shape, as shown in the attached photographs. I would like to understand the possible cause, whether it is age-related osteoarthritis, rheumatoid arthritis, trigger finger or another joint problem.   My questions: 1. What could be the actual diagnosis ? 2. Medicines which can help relieve pain, stiffness and inflammation ?   3. Can it be treated with medicines, exercises, physiotherapy or a splint without surgery? Please review the attached photographs and suggest the best possible treatment, preferably non-surgical, considering my age of 70 years.