In the first episode Simi was 28. When she met Abhi at Kutb Minar, he said he was 5 or 6 years younger than her. This would have made Abhi 22-23. Then later, Manju said that the family had lied about her age in school and she was 3 months from turning 30. That would have made her 29.
At this point I thought KB team would have also increased Abhi's age. If he was 5-6 years younger than her that would have made him 23-24. However, the producers of the show made him 22 which is now 7-8 years younger than Simi. They even had Abhi (if you are watching the show in the US this scene has not happened) say he was 22 and that Simi was 30 (a time span of 3 months has not even happened on the show).
While many of us are not against the idea of a younger guy with an older woman, when the couple is under 30, it's often not plausiable. Had Abhi been over 25 and Simi 32-33, it would not have looked so odd and actually believable. At the age of 23-24, Abhi could be completing his masters and that would have meant he would be doing some research and perhaps even lecturing to make some money on the side (at least that's how it is in the US - you can only lecture when you are working on masters).
As mentioned Hollywood has had a handful of relationships of this kind, the most notable: Heath Ledgetrand Naiomi Watts (he was 24, she was 34) and Cameron Diaz and Justin Timberlake (she was 31 and he was 23). Cameron and Justin did look odd together. Neither couple married.