As a scalable Internet-access network, an Wireless Internet-access Mesh Network (WIMNET) consists of multiple wireless access-points (APs) that are connected through wireless links. At least one AP acts as a gateway (GW) to the Internet where any host must reach there through multi-hop communications between APs. To handle large traffics, the latest high-speed IEEE 802.11ac protocol should be adopted for scalable WIMNET, where the routing path determines the performance under its practical implementations using commercial products. Therefore, we have proposed a routing algorithm considering 1) multiple GWs, 2) the link speed change, and 3) the limited number of hops. In this paper, to further improve the performance, we extend the routing algorithm to efficiently consider the frame aggregation in IEEE802.11ac. We verify the effectiveness of our proposal through simulating two topologies using the extended WIMNET simulator.