We present measurements of ultraviolet Fe II/Mg II emission line ratios for high redshift quasars (z ⪉ 5) in order to estimate the beginning of intense star formation in the early universe. A detailed comparison of these quasars at high redshifts to composite spectra of quasars at the same luminosity but lower redshifts indicates a lack of evolution in the Fe II/Mg II ratio and, by inference, the Fe/Mg abundance ratio. Nucleosynthesis and stellar evolution models predict that α-elements like Mg are produced by massive stars ending in type II SNe, while Fe is formed predominantly in SNe of type Ia. Guided by the resulting iron enrichment delay of ˜ 0.3 - 0.6 Gyr, we tentatively conclude that major star formation activity in the host galaxies of our high-z quasars must have started at zf ≃ 6 - 9, when the age of the universe was ˜ 0.5 Gyr (Ho = 72 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7).