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Measurements of stellar properties of galaxies when the universe was lessthan one billion years old yield some of the only observational constraints ofthe onset of star formation. We present here the inclusion of\textit{Spitzer}/IRAC imaging in the spectral energy distribution fitting ofthe seven highest-redshift galaxy candidates selected from the \emph{HubbleSpace Telescope} imaging of the Reionization Lensing Cluster Survey (RELICS).We find that for 6/8 \textit{HST}-selected $z\gtrsim8$ sources, the $z\gtrsim8$solutions are still strongly preferred over $z\sim$1-2 solutions after theinclusion of \textit{Spitzer} fluxes, and two prefer a $z\sim 7$ solution,which we defer to a later analysis. We find a wide range of intrinsic stellarmasses ($5\times10^6 M_{\odot}$ -- $4\times10^9$ $M_{\odot}$), star formationrates (0.2-14 $M_{\odot}\rm yr^{-1}$), and ages (30-600 Myr) among our sample.Of particular interest is Abell1763-1434, which shows evidence of an evolvedstellar population at $z\sim8$, implying its first generation of star formationoccurred just $< 100$ Myr after the Big Bang. SPT0615-JD, a spatially resolved$z\sim10$ candidate, remains at its high redshift, supported by deep\textit{Spitzer}/IRAC data, and also shows some evidence for an evolved stellarpopulation. Even with the lensed, bright apparent magnitudes of these $z\gtrsim 8$ candidates (H = 26.1-27.8 AB mag), only the \textit{James Webb SpaceTelescope} will be able further confirm the presence of evolved stellarpopulations early in the universe.

Stellar Properties of z ~ 8 Galaxies in the Reionization Lensing Cluster Survey