Is it possible to build a patio using an old above ground pool base?

There is probably plenty of sand there to get started. However, you will want to raked this area clean, define the area where the patio will be placed and follow the usual directions on laying a patio. You may have to either dig out some sand or add some sand to make it ground level.

However, make sure your area is pliable so you can level as you work! You do not want hard packed sand!

Drown the area with vinegar to get rid of the weeds. Here is how to lay a paver patio.

This has some great info on the prep and installing of a paver patio, usually there's more than just sand underneath but your area and current sand look liek they'll work in fine and would love to see photos when you're done! https://www.diynetwork.com/how-to/skills-and-know-how/masonry-and-tiling/how-to-install-concrete-pavers

I wish I could help you more, but in my case, I left the walls up (on my 24' round pool, with a deck and walk around area)....and I'm going to make a sunken den out of it...lol...with lawn chairs in there, as well as twinkle lights, plants and a BBQ pit!! When life gives you lemons, make a beach out of it!!...:) Taking mine down wasn't an option for me (too expensive and it would involve extending the existing fencing, etc)....but I think your idea of using pavers to make a patio should work out well for you!! Good luck!!

I use to have an 18 foot above ground pool. Once my kids moved out I was stuck with a 22 foot diameter area on a hill that was terraced with railroad ties. I extended the area a little on one side so I could plant a flower garden, planted hydrangeas around the rest of perimeter, built a fire pit in the center, planted some grass, and my son put in a circular path with pavers (mother’s day gift). It’s very pretty and looks like it was designed especially for this area

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Your about one third there. Get rid of the weeds, level and compact the sand. Usually landscape fabric is under the sand to prevent weeds, but if you sweep polymeric sand into the paver joints once laid you shouldn't have a problem.