How long do Viera live?

[Vuekkun]

Talk to the Wandering Dramaturge on the Prima Vista in Kugane:

For the Viera, the hands of time move at a far more leisurely pace than they do for the rest of us. Whereas a Hyur might consider themselves fortunate to see, say, eighty winters before her return to the Lifestream, a Viera can endure up to twelve score or more. It is estimated that upwards of eight in ten Viera are born female, though it is not until at least the thirteenth nameday─when the individual moves from adolescence into adulthood─that the individual’s gender becomes apparent. Then, for the next two centuries will the Viera maintain its physical youth, rendering it nigh impossible to discern one’s age simply from outward appearances.

Twelve score is 240, btw.

So, does this quote imply that after 13 years, they grow discernible and simply stop aging? Or does it mean that when a Viera becomes the equivalent of a human 13 year old (which would mean many more years have passed in actuality) they grow discernible?

TLDR; do they turn 13 and stop aging or do they just age really slowly?

Apologies if I’m not making any sense