Mousehole is lovely. Very picturesque, small village/hamlet & popular with tourists. But really not much there. A lovely tea room / deli, couple of small gift shops, ice cream, pub, couple of restaurants, nice chippy, few art galleries ...... and a very small beach on the harbour. (More a patch of sand than a beach compared to other places in Cornwall), and another more pebley beach on the Newlyn side of Mousehole (good for rockpools). In my opinion it would probably suit very young families, but not really enough for teenagers.
You'd need to travel further afield for a surfing beach / or for body boarding etc. We visit regularly, but to be honest a few hours is plenty for us as we like a little more to do. It's a great base if you are happy to drive and visit elsewhere in Cornwall, and there are some lovely walks nearby. (The one to Lamorna Cove is fab!)
Bear in mind the streets are narrow and parking is limited, so if you do stay there make sure you will have a parking space.
From memory, the nearest surfing beaches would be Praa Sands or Porthcurno. Or you could travel across to Sennen Cove, or even drive to the St Ives Bay area where there are lots of surfing beaches within a few miles.