Close to 200 years. In the one episode where Sarek is delusional they talk about how Sarek & Picard mind melt so that Sarek may complete a difficult peace treaty. Then Picard goes to Sarek to find out about Spock on Romulas. Sarek dies before Picard finds Spock.
Sarek was 102.437 years old in ST:TOS "Journey to Babel", and Vulcans are known to live 250 years ProfessorTrek 19:17, August 17, 2011 (UTC)