I started 2 and a half years ago as part of a weight loss plan. I was 48 years old, had done no competitive sport in my life, was far too heavy and took very little exercise. Yet for some reason I wasn't desperately unfit. I see some people saying they were struggling in the beginning to do a mile. I started with 10s and built it up to 30 within the first month.
I showed steady progress up until December last year and then mainly because of bad weather and partly because of a run of punctures I backed off quite a bit and my fitness/ speed dropped.I'm back with a vengeance in the last month and its picking up again now but having my first real setback was disheartening.There will doubtless come a point where the hard work and slow progress make me wake up to the fact I'll never enter the Tour de France, and question whether it is worth it, but I want to delay that as long as possible.
I think its very much about how much you want it. I've had to work at it like nothing I've ever done in my life before. It also has to fit into the rest of my life. I've a pretty busy job, with some irregular hours. I've a family who are well on their way to growing up but still need a fair bit of time, and bizarrely and slightly reluctantly we got a dog last year. Its amazing how much of a hole he can make in cycling time.
People cycle for different reasons. Speed is very high up my list. Never having done it before I want to test myself against others. 20 mph is a magic number for me. Hitting 20 on the flat for the first time, averaging 20 for a mile and then doing the same for 5 miles were all significant milestones.
I am getting decent miles in so maybe if I can keep it going I will see a little bit more improvement yet.
It is the odd good day when things seem to feel right that keep most of us motivated I think. Makes up for the days when I feel like I am cycling through treacle 
