Excessive ageing can affect a tyre's performance and even its roadworthiness.
That's why there isn't necessarily a link between the age of a tyre and wear since it depends entirely on how it has been stored and used.
For example, a new tyre parked or stored next to an electrical substation could show signs of irreversible damage (cracking) to the sidewalls after just a few days. This would affect its performance and tyre pressure.
If the legal or technical limit wear limit has been reached at one point on the tread, the tyre must be changed.
The technical limit is shown by the tread wear indicators (0.8mm on MICHELIN tyres). The legal limit, when there is one, takes precedence over the technical limit (as it is usually stricter).
Tyres are made from rubber-based materials and compounds since their properties are an essential part of a tyre's job.
These properties change over time and may depend on a variety of factors to which the tyre is subjected throughout its useful life: weather, storage conditions, usage (load, speed, pressure…). The factors involved in wear are so variable that it is impossible to predict exactly how long a tyre will last.
Have your motorcycle/scooter tyres checked from time to time by a qualified professional in addition to your own regular checks.
After 5 years of use, have your tyres checked annually.
After 10 years of use, as a precationary measure, replace your tyres with new tyres even if they appear to be in a satisfactory state and even if they haven't reached the legal tread wear limit. This precautionary measure should also be applied to inner tubes and rubber accessories (rim tape...), except if the manufacturer indicates otherwise, as for the MICHELIN Bibmousse.