I realise that your Joseph Impey is one more generation older than mine, but maybe mine is a son, nephew or cousin of yours?
There are at least seven Impeys buried in the Eastern Cemetery at Geelong (Victoria, Australia). The oldest one is a Joseph Impey who was a coach painter. He married (Ann Strange born in Dublin about 1822) in Tasmania in 1841 and came to Geelong some time after that. His daughter Mary Ann was married in Geelong and buried under her married name (at 70 years old in 1913). His son Joseph was also buried there at the age of 67 in 1915.
The cemetery records say Joseph Impey was born in Bedfordshire and was 71 years old (at the time of his death in September 1873), which makes him born around 1801/1802, but the Tasmanian government http://resources.archives.tas.gov.au/pioneers/taslink3.asp?ID=193386http://resources.archives.tas.gov.au/pioneers/taslink3.asp?ID=193386 pioneers record lists 1811 as his year of birth. http://resources.archives.tas.gov.au/archmarriage/default.asphttp://resources.archives.tas.gov.au/archmarriage/default.asp Index to Convict Applications For Permissions to Marry gives the name of the ship "Chapman" which brought him to Tasmania, and also lists Ann as being "free".
I am still looking for information about the 'Chapman', which apparently came in 1824 and 1826 with convicts. (This is the only convict ancestor I have found! ;) All the rest were free settlers, so far.)