In the other thread "Kewley of The Braide Marown" 23/3/2016 8:30am, you'll see I've solved this one at least to my satisfaction.

Robert is from The Braidd, Marown, as I speculated. He's son of John Kewley of The Braid and Alice, per his 1725 Marown will recently summarized and posted on MNB by Frances. Robert's baptism is missing but he must be a younger child, because he lived to 1784. I picked "ca 1703" which makes him the youngest in the family, but quite a bit older than the estimated "c. 1714".

Robert's grandparents fit well to be John Kewley & Alice Crellin whose will extracts 1685 & 1688 were just added by Frances.

And at last, with great ceremony, I declared my ancestor Robert b ca 1737 to be the son of Robert K & Ann Garrett. So I've gained some new ancestors and a hole in my genealogy patched.