I thought average was 6.3 inches. However, I'm thinking that this mmust be a very unfortunate series of events purely because I know for a fact that people here may be hung, but most of that is due to Penis Enlargement. Several people at these forums started off with 5 or 5.5" dicks. Either your mates are lucky or the women are lying (which is quite possible). His 6 1/2 inches limp could well have been a semi-erection, mine measures over 6.
Also I can't really picture a woman pulling out a ruler before she shags a bloke so it may well have just been their estimation, which, as we have discussed here before, is quite often well over what the real measurement is.
Don't worry. Most men here feel insecure with their size even if they are huge. Keep Pe'ing and its quite possible you could catch up with your friends. Samzman on this forum started at 5.5" and (quite an inspiration) grew to just under 9.5".