Thanks for your comment about my swimming. I have been swimming for years and have done the Swimathon (5,000m) 6 or 7 times since 1991. I completed the first one (200 lengths of 25m pool) in 2 hours 15 minutes and finished last year's in 1 hour 52 minutes. When I was at university in 2006/7 I trained with the university swim team although I couldn't compete in their team as I was too old. Since then I have continued to train using the Swimfit training plans (they have 4 different levels - shape and tone, health, fitness and competitive) during the winter and go running in the summer. I do a mixture of front crawl (that is now my dominant stroke) and breast stroke.
Your distance/time of 64 lengths in 55 minutes is nothing to be sniffed at and with practice will get better.