I assume you are asking about the minimum age "requirement" for children to be a passenger in a sidecar, versus an age "limit" when someone is too old to ride.
The answer is that it varies by state in the US and by country in Europe. The range of restrictions can be from no minimum age requirement to the highest I have found being Washington state's 5 year old requirement.
The only way to find this is to check with the states you ride in. Worth mentioning that these are ridiculous laws and are widely ignored. Probably most officers arent aware of such trivial things and even more unlikely to pull you over to enforce it.
This depends upon which state you are operating the motorcycle in.
No, there is no limit in MS.
16 is the legal age
If you have the money, any age. Riding it is a different matter
You can learn from as young as 13
England does not impose an age limit for riding pillion on a motorcycle so long as the driver holds a full driving licence for two years.
The limit differs from state to state. If you pass all of the written and driving tests, you can get a motorcycle endorsement at 18 in most states.
3
There is no age restriction
15 years
13
There it's no limit to age but any passenger under 18 is required to wear a helmet