I'd say it looks like it resets the aging clock. You could indeed consider that you then nevertheless die when your time is up - but that seems pretty weird to me, and I wouldn't. There's a maximum of +3 on the mental enhancers anyhow, so I don't think it'll be game breaking even should it some occur that someone abuses this (which you don't want to allow of course, as DM, but it's not the end of everything). There are a lot of balancing factors, such as the level loss, the cost, and the impossibility of choosing your own body.
Game-play wise, reincarnate has a bunch of other open ends anyhow, such as how to deal with racial HD, level adjustments, racial abilities etc. Just add this to the bunch - the spell is thoroughly in the plot-advancement region anyhow, and that means it'll need individual adjudication each time anyhow.
Indeed, this looks like a fun plot hook possibility!