Usually, the maximum period that you can register a domain for, is 10 years. However, there can be a different limit set by providers, or by a specific domain. Also, if you register the domain for 2 years on a signup, then you can renew it for maximum 8 years more, the total period can't exceed 10 years anyway.
That is correct. A maximum of 10 years at a time. I'm unaware of the ability to go beyond that unless a company is taking your money and holding it until they can manually renew it in the years to come.