It may have been mentioned in the first season but I can't recall..
I believe they say she is 29. Ellie Kemper is really 36 I think but she exudes so much youth and looks great so it's believable.
She turned 30 in season 1.
Yeah she was still 29 when she left the bunker, and then had her 30th birthday party in season 1 episode 9. So if we're to assume season 2 was the next year then she is now 31.