includes a photo of his gravestone with the inscription: 'Here lies Interr'd the remains of Doct. David Strong, who died Sept. 11th 1807. In ye 83d Year of his Age.'
"in the 83d year of his age" means he was 82, consistent with a birth date of May 1725. (May 1725 is also the year that fits best between his siblings' birth dates.)