Deep rest-optical observations are required to accurately constrain the stellar populations of z similar to 8 galaxies. Due to significant limitations in the availability of such data for statistically complete samples, observational results have been limited to modest numbers of bright or lensed sources. To revolutionize the present characterization of z similar to 8 galaxies, we exploit the ultradeep (similar to 27 mag, 3 sigma) Spitzer/Infrared Array Camera (IRAC) 3.6 and 4.5 mu m data, probing the rest-frame optical at z similar to 8, over similar to 200 arcmin(2) of the GOODS fields from the recently completed GOODS Re-ionization Era wide-Area Treasury from Spitzer program (GREATS), combined with observations in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)/Ultra Deep Survey (UDS) and CANDELS/Cosmic Evolution Survey (COSMOS) fields. We stacked greater than or similar to 100 z similar to 8 Lyman-break galaxies in four bins of UV luminosity (M (UV) similar to -20.7 to -18.4 mag) and study their H (160) - [3.6] and [3.6]-[4.5] colors. We find young ages (less than or similar to 100 Myr) for the three faintest stacks, inferred from their blue H (160) - [3.6] similar to 0 mag colors, consistent with a negative Balmer break. Meanwhile, the redder H (160) - [3.6] color seen in the brightest stack is suggestive of slightly older ages. We explored the existence of a correlation between the UV luminosity and age, and find either no trend or fainter galaxies being younger. The stacked SEDs also exhibit very red [3.6]-[4.5] similar to 0.5 mag colors, indicative of intense [O iii]+H beta nebular emission and star formation rate (SFR). The correspondingly high specific SFRs, sSFR greater than or similar to 10 Gyr(-1), are consistent with recent determinations at similar redshifts and higher luminosities, and support the coevolution between the sSFR and the specific halo mass accretion rate.