Hello ktkeith,
I have connections to this family and will see what I can find for you. It is probable that the name has been mistranscribed in the 1841 census.
I have some Thelwell family in a later census that are shown as Thalwiser!
The 1841 census should have ages rounded up, or down, to the nearest 5 years. So William Thelwell would be shown as aged 35, in theory anyway.
Jo