Looking at the index to the 1861 census on SP, I see that in Lochalsh, enumeration district 3, page 9 there are
Kenneth Matheson, 44; Margaret Matheson, 40; Donald Matheson, 19; John Matheson, 12; Rory Matheson, 10; Donald Matheson, 7; Johnnie Matheson, 4; and Kenneth Matheson, 1.
I also note that Kenneth Matheson and Margaret Matheson had John, born 10 April 1857 and Kenneth, born 28 January 1860.
So it looks to me as if Donald Matheson, born 1842 and baptised 1843, may still have been with his parents Kenneth and Margaret in Lochalsh in 1861. If so, then obviously he isn't the one you are looking for. A look at the original of the 1861 census on SP would confirm or refute that.