Aging, the gradual changing of materials properties with time, is a well observed but puzzling phenomenon in ferroelectrics. It lowers the reliability of ferroelectric devices, and is thus usually undesirable. However, based on a defect mediated reversible domain switching mechanism, we obtained large recoverable electro-strain in aged BaTiO 3-based ferroelectric crystals, which indicates aging is not always a detrimental effect; it might be beneficial for applications. Moreover, direct evidence for the reversible domain switching process was given by in situ polarizing microscope observation. The underlying microscopic origin was discussed in light of a symmetry-conforming short-range-order (SC-SRO) principle of point defects and electron paramagnetic resonance spectroscopy.