  We present the characterization of the low-gravity M6 dwarf 2MASS J0619-2903
previously identified as an unusual field object based on its strong IR excess
and variable near-IR spectrum. Multiple epochs of low-resolution (R~150)
near-IR spectra show large-amplitude (~0.1-0.5 mag) continuum variations on
timescales of days to 12 years, unlike the small-amplitude variability typical
for field ultracool dwarfs. The variations between epochs are well-modeled as
changes in the relative extinction ($\Delta{A_V}\approx2$ mag). Likewise,
Pan-STARRS optical photometry varies on timescales as long as 11 years (and
possibly as short as an hour) and implies similar amplitude $A_V$ changes.
NEOWISE mid-IR light curves also suggest changes on 6-month timescales, with
amplitudes consistent with the optical/near-IR extinction variations. However,
near-IR spectra, near-IR photometry, and optical photometry obtained in the
past year indicate the source can also be stable on hourly and monthly
timescales. From comparison to objects of similar spectral type, the total
extinction of 2MASS J0619-2903 seems to be $A_V\approx4-6$ mag, with perhaps
epochs of lower extinction. Gaia EDR3 finds that 2MASS J0619-2903 has a
wide-separation (1.2' = 10450 AU) stellar companion, with an isochronal age of
$31^{+22}_{-10}$ Myr and a mass of $0.30^{+0.04}_{-0.03}$ Msun. Adopting this
companion's age and EDR3 distance (145.2$\pm$0.6 pc), we estimate a mass of
0.11-0.17 Msun for 2MASS J0619-2903. Altogether, 2MASS J0619-2903 appears to
possess an unusually long-lived primordial circumstellar disk, perhaps making
it a more obscured analog to the "Peter Pan" disks found around a few M dwarfs
in nearby young moving groups.
