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Upon its discovery in 2006, the young L7.5 companion to the solar analog HD203030 was found to be unusual in being $\approx$200 K cooler than older late-Ldwarfs. HD 203030B offered the first clear indication that the effectivetemperature at the L-to-T spectral type transition depends on surface gravity:now a well-known characteristic of low-gravity ultra-cool dwarfs. An initialage analysis of the G8V primary star indicated that the system was 130--400 Myrold, and so the companion between 12--31 $M_{\rm Jup}$. Using moderateresolution near-infrared spectra of HD 203030B, we now find features of verylow gravity comparable to those of 10--150 Myr-old L7--L8 dwarfs. We alsoobtained more accurate near infrared and {\sl Spitzer}/IRAC photometry, andfind a $(J-K)_{\rm MKO}$ color of $2.56\pm0.13$ mag---comparable to thoseobserved in other young planetary-mass objects---and a luminosity oflog($L_{\rm bol}/L_{\odot}$)$\,=\,-4.75\pm0.04$ dex. We further reassess theevidence for the young age of the host star, HD 203030, with a morecomprehensive analysis of the photometry and updated stellar activitymeasurements and age calibrations. Summarizing the age diagnostics for bothcomponents of the binary, we adopt an age of 100 Myr for HD 203030B and an agerange of 30--150 Myr. Using cloudy evolutionary models, the new companion agerange and luminosity result in a mass of 11 $M_{\rm Jup}$ with a range of 8--15$M_{\rm Jup}$, and an effective temperature of $1040\pm50$ K.

The Prototypical Young L/T-Transition Dwarf HD 203030B Likely Has Planetary Mass