Neutral atomic hydrogen (HI) is thought to be the principal reserve for the formation of stars and the triggering of active galactic nuclei (AGN). However, until now, epochs between 0.4 allow us to carry out the first radio-selected 21cm absorption surveys during this period of cosmic history. Using the six-antenna Boolardy Engineering Test Array (BETA) of the Australian SKA Pathfinder, we are carrying out a search for 21cm absorption towards a sample of the brightest and most compact radio sources in the southern sky. We have recently made our first discovery of HI gas towards a gigahertz peaked spectrum (GPS) radio source at z = 0.44, with follow-up optical spectroscopic observations (using Gemini South) confirming that this absorption arises from gas in the host galaxy. Analysis of the gas kinematics using radio and optical spectroscopy indicate that the neutral and ionised gases are outflowing at more than 300km/s. We infer that the young radio AGN is expelling gas from the circumnuclear medium at more than 1M_solar/yr. This result is very encouraging for imminent wide-field absorption surveys to be carried with the SKA precursors, which we predict should detect many such intrinsic systems, as well as constraining the evolution of the cosmological HI mass density at moderate redshifts.