I have very successfully painted over 30 year old walnut wall panelling. I started by filling the grooves with a flexible polyfil/joint compound. Next I rolled on a textured paint by Behr using a "loop" roller. After applying the textured paint, I waited about 20 minutes and went back with my trowel and sort of smoothed and textured the paint so it looked like a tuscan wall finish. It took approximately 24 hours to dry. Then I did some touching up with the textured paint, (filled more grooves where I may have missed). Finally I painted with a rough surface roller the paint colour of my choice: Benjamin Moore - Dijon for me. The final product is pretty amazing. You would never know there was wood panelling behind the paint. The finish is very mediteranean looking and in keeping with the age of my house. good luck.