There is a John Shimmin 67 widower in the 1851 census in Linage Rushen HO107/2526 folio 259 page 13.
John Shimmin Widower 67 Farmer 10 acres b Rushen
James Lowey 43 son-in-law b Rushen
Ann Lowey 37 daughter b Rushen
Isabella grandd 3 b Rushen
Ann 4 grandd b Rushen
John 2 Grands b Rushen
The IGI has an Ann Shimin, daughter of John Shimin and Catherine Bell, christened October 10 1813 and an Ann Shimmin who married James Lawey in Rushen on Feb 13 1844.
This may be your John. If so he was born 1783/4.
The IGI has Jno Shimmin, the son of Jno Shimmin and Ann Kewn, chr. Rushen Sept 17 1783.
I would check the wills.