With the given details it can be arthritic changes. The reason for that can be due to collapse of the arch/es of foot or chronic ligament sprains. Consult with  a Physiotherapist who can assess and help you in regaining mobility with appropriate exercises and mobilization procedures.  As a home remedy you may try exercises ( forward and backward, sideways, clockwise  and anticlockwise tilts) on a wobble board in sitting and later in standing.