In Season 6 Episode 3, New Ron, when leaving said, "Taurus' and Capricorns just dont mix huh." We know that Ron was born in springtime, which starts march 20th. A Capricorn, which is from december 22nd to January 22nd, does not fit into this. A Taurus however, which is from April 20th to May 20th, does. Meaning this is his both date age range. We can narrow it down further due to Leslie asking if its his birthday on Friday. Meaning we can narrow it down to all Fridays in that range, in that year, 2011, which are, April 22nd, April 29th, May 6th, May 13th, and May 20th.