The Thomas you mention is the only one in the IGI who was christened in Patrick between 1792 and 1796.
In the IOM 1851 census there is a Thomas Shimmin Age 59 in Patrick aged 59, Widower Farm labourer, living with his daughter, Elizabeth.
His birthplace is given as German.
The oldest Thomas Shimmin the 1851 census for England was aged 32.