Re: cadence - why can't I peddle faster and do I really need to?

Hi,
First time poster, sorry if it's in the wrong place on the forum.

I read and hear that a cadence of 90+ is the most efficient rpm for cycling. I've been riding a bike, mtb and road for most of my life, but occasionally competitively for the last 15 years. I'm now 40. On the turbo I struggle to get over 80rpm at a constant power output - looking at what I'm doing on long climbs I'm lucky to average 65rpm. Riders that I ride with at the same sort of pace are up in the high 80's, low 90's. If I drop a gear or 5 and try and match their cadence I get lactate building very quickly and I drop off the pace.

I've a mate who has just started riding and I've given him some 'advice' he we'll over a 100kg and my age. His can maintain a cadence of well over 90 on the trainer and on the road. What gives?

Watching old clips of riders in the late 80's of earlier the cadence seems much slower (ie lemond). My question is, do I really need to focus on my hideously slow legs? Or do I just ignore it. I don't get as many knee problems as I used to and wonder if I'm just not physiologically able to increase my cadence that much. I've tried in small increments (like trying to ride at 81rpm, rather than 80 rpm on the trainer) but hit a lactate brick wall on every attempt, and as it's painful to try it reduces my motivator to carry on.

Any ideas?