Chipy,
You can search the 1871 census yourself on ScotlandsPeople. This is a pay-per-view site but the charges are (in my view) reasonable. I note, from the free search on that site (one needs to register but that is free), there is only one William DICK in the 1871 census in Paisley and he is the right age (25). If your William remained in Paisley, this could well be him.
You say that William DICK was born about 1845 in Paisley, Renfrewshire of parents David & Agnes.
If he is the following, then you have more precise information from extracted entries in the IGI on the (free) FamilySearch site - William DICK, parents David DICK & Agnes MCKAIG, b 16 Jun 1845, bap Jul 1845. The same parents (married 23 Aug 1844 in Paisley) also had John b 26 Mar 1849, Agnes b 29 Apr 1851, David b 9 Dec 1855, Grace b 19 Jun 1853, Sarah b 8 Jun 1859.
JAP