Well, he doesn't seem to be from Dunoon! The only Thomas Forsyths I can find in the right time period are:
Thomas Forsyth son of James Forsyth and Margaret Pope born on 17 May 1815 at UDNY, ABERDEEN, SCOTLAND
Thomas Forsyth son of Alexander Forsyth and Jane Symmers born on 5 April 1810 at FINTRAY, ABERDEEN, SCOTLAND
Thomas Forsyth son of John Forsyth and Mary Trotter born on 28 April 1801 at LANGTON, BERWICK, SCOTLAND
Thomas Forsyth son of Thomas Forsyth and Agnes Chisholm born on 19 September 1806 at STOW, MIDLOTHIAN, SCOTLAND
Thomas Forsyth son of Bezaliel Forsyth and Kathrine Mitchell christned on 1 April 1816 at Middlebie, Dumfries, Scotland
Thomas Forsyth son of James Forsyth and Elisabeth Galbraith born on 24 April 1806 at WHITTINGEHAME, EAST LOTHIAN, SCOTLAND
Thomas Forsyth son of David Forsyth and Betty Mclagan born on 4 August 1815 at KINNOUL, PERTH, SCOTLAND
Thomas Young Forsyth son of William Forsyth and Barbara Murray born on 17 March 1814 at BARR BY GIRVAN, AYR, SCOTLAND
Thomas Forsyth son of James Forsyth and Mary Whannell born on 19 October 1817 at GIRVAN, AYR, SCOTLAND
Thomas Forsyth son of John Forsyth and Isabela Gilchrist born on 27 May 1816 at LIVINGSTON, WEST LOTHIAN, SCOTLAND
Thomas Forsyth son of James Forsyth and Jean Walkingshaw born on 4 May 1809 at TORPHICHEN, WEST LOTHIAN, SCOTLAND
Thomas Forsyth son of Thomas Forsyth and Janet Andrew born on 22 December 1801 at GLASGOW, LANARK, SCOTLAND
Thomas Forsyth son of Thomas Forsyth and Robina Aird born on 19 March 1802 at MAYBOLE, AYR, SCOTLAND
Thomas Forsyth son of John Forsyth and Isobel Laird born on 16 May 1814 at SHOTTS, LANARK, SCOTLAND
Thomas Forsyth son of George Forsyth and Margaret Borrowman christned on 21 October 1810 at Larbert, Stirlingshire, Scotland
Thomas Forsyth son of William Forsyth and Margret Wood born on 18 May 1801 at DUMBARTON, DUNBARTON, SCOTLAND
The closest to Dunoon is the last one who was born 27 miles away...and about 10 years too early!
Now, how to whittle down this 16 to try and find my 'one'...