I have since found that the when the 1841 Census was taken, the
clerks were instructed to round the peoples ages down by increments of 5. This would mean that if a person was aged 59 at the time of the census it would be
recorded as 55 and so on.
Errors were inevitable as in other forms of data collection.
Other inaccuracies would have occurred due to the literal capability of the person recording the information.
From time to time people being recorded when asked their age would have been liberal with the truth.
Also if people were visiting relatives on the day the census was being taken, may have been recorded as living at that address.
This does throw light on quite a few of my own data records and
clears up a lot of speculation.