It doesn't seem very rigorous scientifically to me, more a matter of opinion. Any serious study would have a list of reference sources at the end, which any interested reader could delve into themselves.
Whist you can't argue against a trend of gradual performance decline with age, it doesn't say much about individual fitness. That's the biggest factor, IMHO. I'm not fast on a bike and have no wish to be, but I do have decent stamina and can keep up physical activity at a moderate intensity for a sustained period without looking like I'm going to keel over.
I've had youngsters at work tell me they wanted to stop in the middle of a physical task because they were tired, and on the other hand someone I work with who is 14 years older than me can match me for work effort all day long with no complaining at all.
It boils down to whether you have an active or inactive lifestyle, regardless of whether the activity concerned happens to be cycling or something else. People who move around a fair bit under their own power tend to be in much better physical shape for their age than the general population.