Some old laptop only has 2.4GHz wifi and even have 5Ghz also will not get > 100 Mbps. Better get a AC adapter and it should provide ~ 300Mbps. It is quite cheap too. It is available in many shops. Going for AC adapter is the only choice to enhance his speed.
In the old days, it was simple. 802.11g, you get 54 Mbps, 802.11b, you get 11 Mbps.
But once it comes to 802.11n, there are different speeds like 150 Mbps, 300 Mbps, 450 Mbps and even 600 Mbps. And when device makers say my device is 802.11n, hmm, it's hard for consumers to know what speed they can expect. And then of course, now there is the talk about theoretical speed in laboratory conditions, and actual real world speed. Just surprised that real world speed is only about half of the theoretical one.