I think the best descent from the Old Man is the Torver race route - due south from the structure on the top - the steps point in the right direction, or towards Beacon tarn in the distance if it is clear - a path/trod very quickly appears under your feet - it wanders around a bit but if you get it right it is 95% runnable grass - you end up just above the junction of the Walna Scar track and the path leading to Goat's water.