Peebee's Age

possibly got more to do with her impulsivity. She's almost the opposite of Liara personality wise.

I've heard that she's the equivalent of a Human 19-20 year old, so, that places her at probably a little over 100 I think. It'd make sense given her behavior.

She's very non-asari when it comes to the majority of her behavior. But I like it. Sara is very different from FemShep too. She wouldn't click with Liara but she does with PB.

There's no way she's 100 years older than Liara. I mean, maybe she's just petite but... she seems younger overall.

PeeBee gives us her age range in a banter with Drack. She says she is 100 and some change.

I don't see the mistake there. If you are referring to her sister being five hundred years older, PeeBee has a banter with Drack about that too, namely her mother had her very late in life. 

1:18 for the one with her mother having her late.
5:15 for the one with her saying her age.

Peebee could be 149 and still round it down to "100 and change" and her sister could be 549 years older and that difference still be rounded down to 500 years.  So, PeeBee's sister could be very near 700 years old without there being any lie or mistake... just rounding/approximation.  Liara says she is "considered to be barely more than a child."  That doesn't say that she is actually a child or a teenager.  It only really says, in context, that her work and opinions are viewed by her older colleagues to be immature.  The references are also probably being adjusted so the reader gets a sense that the Asari think in centuries, not years"  So, where a few years makes a difference to humans, even as many as 50 years to an Asari makes little difference to them.  Additionally, the time of life at which different cultures consider "passage into adulthood" varies and it has historically changed over time.  There have also been some variances based on economic class.