There are an awful lot of John Milnes in Aberdeenshire! You must know more about him than just his years of birth and death, otherwise you wouldn't be asking. You will stand a much better chance of getting help here if you supply a bit more of the basic and easily accessed information.
Where was he born, where did he die, whom did he marry, and what were the names of his children, who were his parents?
If you have not already done so, and assuming that he died in Scotland, you need to start by going to
www.scotlandspeople.gov.uk, investing in a few credits at modest cost, and using one credit to find and 5 to download an image of his death certificate. This will tell you the name(s) of his wife/wives, and of his parents, including his mother's maiden surname.
Once you know the name(s) of his wife/wives, you can go to
www.familysearch.org and use this information to look for names and dates of baptism of his children. The original documents indexed on Family Search can be viewed on Scotland's People.
You should be able to find transcriptions of the 1841 and 1851 at
http://www.freecen.org.uk/cgi/search.pl, and (depending on which parish they lived in) the 1861 census records. Again, the originals are on Scotland's People, which will also have the 1871 census.
