Its a hard thing to quantify, if i think back through my bikes, my speed overall hasnt changed much, so i wouldnt expect a massive change.
Even then, its difficult to remember how hard a ride was on an older bike compared to more modern ones.
Heavy Raleigh cro mo framed 8 speed racer..i always averaged around 15.5 mph, whatever the distance at the age of 40 ish.
Moved up to an alloy 9 speed bianchi, no great difference in average speed, but the bike was more pleasurable to ride, a bit easier on me.
Next up to a 10 speed bianchi...but now i'm 50, but still averaging the same 15.5 mph with relative ease, whatever the distance.
Now on a full carbon job, at nearly 54, i find myself despite having a lean last 6 months on the bike, still averaging 15,5 with ease, upping to 16.5 if i push along a bit. Thats surprised me, for instance i rattled along at 17mph today on the headwind sections of my 3 mile circuit. Granted because its a short circuit, i 'm quickly moving from side, to tail, so side, to headwind all the time so you do get a rest, but my headwind riding has been very good lately. Is it my new carbon jobby ?...or am i just in a good place physically at the moment ?
A lot of musing, not much to go on, Is a lot of it mental, new bike, new vigour ?
So ive moved from a heavy 8 speed, cheap wheeled raleigh to a full carbon framed, Fulcrum 5 wheeled bike in almost 15 years, i'm still the same where my averages are concerned, but a heck of a lot more comfortable doing it..and with a bigger grin.