As I figured, the suggestion that only mature people would be agreeable to going topless hit them in a sensitive spot; one of the things I'd learned over the years was that pubescent girls almost always want to believe they're more mature and adult than they really are.

But I changed the subject to something else, and we chatted for another few minutes; when their was a lull in the conversation, Emma looked at me, then her sister, before reaching back and unfastening the top of her bikini — then removed it and set it aside. A few moments later, Gail did the same thing, leaving me sitting there with clear views of two pairs of firm young mammaries. I didn't make any big deal out of what they'd done, however. I just smiled at both of them, then went back to talking to them as though half-naked teenyboppers was something I saw every day. After a bit, both of them stopped looking quite as nervous; by the time I had to go back to work, they were as calm and relaxed as they could be. Inside my house, I looked out at them and watched as they decided to go for another dip in the pool — without bothering to put their tops back on.

I checked on them a few more times while they were at my place, and they didn't put the tops of their suits back on until right before they went home.

The next time Gail and Emma came over, they were on their own in the back yard; I was busy with a tricky bit of code I was working on. When they first showed up, I noticed that both kept their bikini tops on; but when I looked at them a little later, both had opted to shed them, to my pleasure.

When I went out to check on them, both looked a trifle nervous at first, but when I didn't stare or say anything, they settled down again quickly enough.