Northboy we go here every year. Depending how fast you walk, it takes about an hour (ish) to stroll along the front from the marina at Benalmadena to the bottom of the climb up to Torremolinos town.
We stay on the Carihuela each February (which is the beach between the two resorts and walking from one resort to the other is always part of our holiday. The Carihuela sea front walk is flat as a pancake so ideal for those who find it harder to walk, and plenty of stopping places and cafés along the way, highly recommended.
I don't know about the railway track path that jed mentions, we always walk next to the beach, the views to the Sierra Nevada as you walk towards Torremolinos are stunning.