With the downscaling of CMOS technology, the circuit design margin becomes more and more tight due to wider guardband, which is required to counteract the severer transistor aging and variations. Thus, reliability-enhanced circuit design is urgently needed to reduce the guardband. In this paper, a reliability-enhanced design framework based on approximate synthesis is proposed to completely eliminate the aging guardband. It mainly includes two key parts: first, a forward reliability simulation flow supporting statistical static timing analysis (SSTA) is performed to estimate the path failure rates after aging; if the timing constraints are not satisfied, then a backward delay-driven approximate logic synthesis flow will perform approximate local changes on the critical paths to reduce the delay until the reliability requirement is finally satisfied and no aging guardband is needed. The results show that the approximate circuit has a smaller aged delay than the original circuit, so that the path failure rates are significantly decreased. It indicates that the proposed design flow can convert the timing errors that have fatal impact on applications, into negligible error on low-significance bits to improve the resilience of circuits, which provides a new perspective of reliability-enhanced design at nanoscale.