1. Sport hunting of wildlife can play a role in conservation but can also drive population declines if not managed sustainably. Previous simulation modelling found that large felid species could theoretically be hunted sustainably by restricting harvests to older individuals that have likely reproduced. Several African countries currently use age-based hunting for lions although the outcomes have yet to be evaluated in a wild population. 2. Here we provide the first empirical evidence that a system of incentives sufficiently encouraged age-based hunting and reduced offtake of a wild felid, thereby reducing the potential risk of unsustainable hunting on a threatened species. We examined long-term hunting data and the lion population trend in Niassa National Reserve, Mozambique. 3. To incentivise hunter compliance, a ‘points’ system was developed which rewards operators that harvest lions older than the 6-year minimum trophy age recommended for sustainable hunting and penalises operators that hunt ‘underage’ lions (<4 years). A key component of this system is the ecological application of key physical traits that predictably change with age in order to estimate (by hunters) and validate (by authorities) trophy individuals’ ages pre- and post-mortem, respectively. Analysis of 138 lion hunts and 87 lion trophies from 2003-2015 revealed that after enforcement of age restrictions in 2006, hunters shifted harvests to suitably aged lions (>6 years), from 25% of offtakes in 2004 to 100% by 2014. 4. Simultaneously, the number of lions and percentage of quota harvested decreased, resulting in lower lion offtakes. Following an initial decrease after enforcement of the aging system, the percentage of hunts harvesting lions stabilised, demonstrating that hunters successfully located and aged older lions. 5. Synthesis and applications. Evidence suggests that age restrictions combined with an incentive-based points system regulated sport hunting and reduced pressure on the lion population. We attribute the successful implementation of this management system to: 1) committed, consistent enforcement by management authorities, 2) genuine involvement of all stakeholders from the start, 3) annual auditing by an independent third party, 4) the reliable, transparent, straight-forward aging process, and 5) the simple, pragmatic points system for incentivising hunter compliance. Our study demonstrates that the use of age restrictions can increase the selectivity of sport hunting and lower trophy offtakes to reduce the possibility of unsustainable sport hunting negatively impacting species populations in the absence of reliable estimates of population size. It must be noted, however, that there was no measurable change in the lion numbers over the past decade that could be attributed to the implementation of this policy alone.