Then in the beginning at least there is the risk of extreme social inequality and a gerontocratic ruling class. Only the wealthy will have access to life extension and it may be the wealthy power structures that deny the technology to other people.
Finally, a civilisation made up of long-lived individuals may become extremely risk-averse, with possible consequences of reduced experimentation, creativity and rebellion. They may also turn out a little like what Larry Niven makes of the Puppeteer race: powerful, cowardly creatures, highly ritualistic, paternalistic and soft-totalitarian.