If we follow any time continuum, Olivia should be much younger. In "Jacksonville" ep, when Olivia broke through the "obstacle" while under cortexiphan treatments, she was saving the little girl of her past who was about 3-4.
Also, if you recall the grow chart with the names of Cortexiphan children, Olive was second shortest in height but in this ep, she clearly was one of the tallest.
I do think that more that 6 months have elapse...I am waiting for the transcript of the show to be released. I am thinking that it is 6 months after some kind of event (not when Walter brough Peter back)?
This retcon business is very tricky I suppose.