There was an interesting discussion this morning on Trib Live Radio in regards to 36 year old wide receivers in relation to Pittsburgh Steelers wide receiver Hines Ward this morning and how effective those receivers were at that age. I pulled the numbers that you can see below in the table from Pro Football Reference of receivers that played at 36 years old and also included their AV number for that season. In short, the Approximate Value (AV) method is an attempt to put a single number on the seasonal value of a player at any position from any year. It is not without faults though.
According to the research I did, there have only been 28 receivers that caught at least 1 pass at the age of 36. 16 of those 28 had 40 or more receptions that year and 23 of the 28 had 400 or more yards receiving in that season. All but 7 on the list had a 10 yards per catch average. Half of the receivers listed had an AV rating of 6 or more at 36.
There are no hard conclusions you can draw from this list other than to say that some 36 year old receivers have proven that they can still be effective in the league at that age. Ward has obvious slipped way down the depth chart due to the young receivers in Pittsburgh, and at the best he is a 4th wide receiver now that does not play special teams. Ward is also coming off ankle surgery as well. He recorded 46 receptions in 2011 on 63 targets and 20 of those were good for first downs. His yards per catch was 8.28. Make of this list what you will.
ETA: I have also now added the DYAR and DVOA numbers from Football Outsiders, where available, as a means of comparison. You can read more about what both Defense-adjusted Yards Above Replacement and Defense-adjusted Value Over Average mean right on their website and see the full numbers of all wide receivers dating back to 1992.