pruning climbing roses

I look after this garden for an elderley lady. She has two groups of very old climbers which have become very woody for much of their length. One group are tied by string to the top of a panel fence. They have grown around 9 feet tall and are still producing flowers. My question is can they be pruned now or in the spring? Also they do not appear to be producing many buds to prune to further down the stems, due to the plants age. Whereabouts do you make the pruning cut? Can you just make a cut anywhere on none woody stems. or can you cut back into older woody stems?