NOTA: A terminologia que você está procurando é EOL aka. Fim da vida. Se você procurar por isso e o nome da distro, você encontrará a maioria deles desta maneira.
O CentOS é provavelmente o mais longo que você encontrará. Do FAQ:
trecho: 8. Por quanto tempo o CentOS 5 será suportado?
We intend to support CentOS 5 until Mar 31st, 2017 The current plan is this:
- Full Updates (including hardware updates): Currently to Q4, 2012
- Updates ( including minor hardware updates): Up to Q1 of 2014
Maintenance Updates Q1, 2011 - Mar 31st, 2017
Full Updates
During the Full Updates phase, new hardware support will be provided at the discretion of CentOS via Update Sets. Additionally, all available and qualified errata will be provided via Update Sets (or individually {and immediately} for Security level errata.) Update Sets normally will be released 2-4 times per year, with new ISOs released as part of each Update Set. In the 5.x numbering scheme, the .x is the number of the Update Set.
Maintenance Updates
During the Maintenance updates phase, only Security errata and select mission critical bug fixes will be released. There will be few, if any, Update Sets released.
A maioria das versões do RHEL / CentOS são suportadas por ~ 10 anos.
trecho de página CentOS EOL - Fim da Vida
CentOS 5
- 7 years primary support life; later extended to ten years
- Mar 31, 2017 EOL
- i386 x86_64 support
CentOS 6
- 7 years primary support life; later extended to ten years
- November 30, 2020 EOL
- i386 x86_64 support