Radio galaxies, a subclass of active galaxies, exhibit bipolar collimated outflowing jets that form lobes via interaction with the intergalactic medium. The cessation of active galactic nucleus (AGN) activity in radio galaxies leads them into remnant phase. Remnant radio galaxies (RRGs) are believed to be rare objects as they can be observed over a relatively short period of time before the radio lobes, with no supply of fresh plasma, completely fade away due to radiative and dynamical energy losses. In our recent work, we identified and characterized RRGs using one of the deepest multi-frequency radio observations performed at 144 MHz, 323 MHz, 390 MHz, 650 MHz, 1.284 GHz and 1.5 GHz using LOFAR, uMGRT, MeerKAT and JVLA , in the XMM-LSS field. In our study, we exploited a faint and high redshift regime and unveiled the largest RRG sample till date. In addition, we demonstrated the existence of a substantial population of small angular scale RRGs for the first time. Furthermore, the timescales of remnant phase and AGN duty cycle are vital to understanding the evolution of radio galaxies. Therefore, we have estimated the spectral ages of RRGs by modelling their radio spectral energy distributions (SEDs) using CI_OFF model in BRATS software. This exercise acts as a test-bed for the upcoming planned surveys with SKA and its pathfinder. In this talk, I shall highlight the importance of deep and sensitive multi-frequency radio observations to estimate the spectral ages of RRGs robustly.