I think its just video game magic! Just like why Totec could speak english same thing. I don't think she really has an age in each as its not really stated and I'm not sure if you can really class TRU/TRL in the same timeline as Cores games
Trust me Link in Zelda is far more confusing that Lara
Why are people trying to slot Anniversary before Legend ? Its a remake of the first so if you really want to include all games there is a massive gap between TR1/Anniversary and Underworld so she should be much older in underworld.