She is not that old. It is normal for girls these days to get married later. She's also been busy with her career. Maybe she isn't 100% truthful about her age because in our society women are always pressured to feel as if they have limited "shelf life." If you think about it, it's a disgusting concept.
Also, nobody really asks women for their age (I don't know why!) so it's become this issue of polite conversation, and so women are sometimes taken aback when this question is put to them.
But one thing is true, which is that Manas and Rakhi are not ideal pairing because of the big age gap. A 22 yr old guy is really different from a 28 yr old guy. Manas is mature, but that doesn't mean he can handle every situation as a husband, the way an older guy can.