The best I've had is 170psi on one of my 650's, 120 -150 is common on GL500/Gl650 the bikes I've had. 120 being on the low end - I also have noticed some gauges read low or high - check with throttle held wide open to get good air flow and bike warm for test. If your bike runs fine, don't worry too much.
If the bike is new to you and maybe set for some time. Ride a few hundred miles and recheck.