Recently I've noticed when my cat walk his back leg is a bit stiff and he stamping slightly whilst walking he seems OK in himself not complaining of pain or anything he eats and drink water well he seems to drink more water since the weather got very hot apart from that he is OK his stiff back leg started I noticed since he is started lying down more on the lino in the bathroom to keep cool in winter he lie down on his padded cushion and seems OK. He is 19 years and 3 months old been a very healthy cat only had Cystitis couple of times but was rid of since took him off eating ham. Could you please tell me what you think it is?

Many thanks in advance

Kind regards