Average speeds, do they matter... if you are training to race I would imagine so..... if you are joe bloggs cyclist going out for a fun ride i would imagine not quite so much, there must be so many things that can alter your average speed... road surface (rough seems to slow me down, smooth seems to speed me up) wind speed and direction ( a good head on wind can knock the arse out out your speed ) uphill or downhill ( yet another equation added) and of course if your average is over a couple of nice flat miles or over 30 miles of mixed riding ( it all seems to make a difference ) I am 56 years old and only started cycling again just over 3 months ago after a break from cycling since i was a kid and when i first got on my new bike i thought I have got to be going fast ... must get quicker, my average speeds did go up.. but I am in my mid fifties and should be grateful that i have found cycling again and it hasn't taken long to realise that some of my most enjoyable rides are the ones with my wife pottering around the country lanes or along the coast and stopping off for lunch somewhere.
Below is this mornings ride, head wind in places fairly flat with a few bumps here and there.. average speed 16.5 MPH over 16.8 miles in an hour and one minute.
While tomorrows ride will be a slow paced 25 mile bimble with my wife stopping for lunch ( no worries and all the time in the world )
The way I see it is enjoy what you are doing whether you are racing along or having a relaxing ride, one things for sure is don't get hung up on average speeds as there will always be someone faster out there.... Anyway if i want to go fast on two wheels I will get one of our motorcycles out..