From 1st April public swimming baths up and down the country start to offer free swimming for those 60 and over and 16 or under. It’s all part of the campaign to encourage people to get active or stay active.
I don’t know, but I suspect you’ll be asked for proof of age or you might need to pay a one-off charge for a special free swimmer card (or something like that) that you’ll need to bring with you on each visit. Also check with the pool for times that you can swim for free.
From what I can tell on this page the Wirral is participating – do tell me if that’s not the case.