Regarding the age gap and love and sustainability - here are my thoughts.
Is it a genuine issue in this story? For sure it is. There is no way to sugarcoat it. If it's a town / locality like where Vidhi is living in, people will talk. Her parents would fall apart. She would not be able to handle it. She is way too cocooned in her own little world for her to deal with something like this. I am not saying she is not strong. I am saying her strength has not been tested yet. Dev would feel awkward and insecure. His patience and temper would be tested when Page 3 keeps bringing up their age. Courtesy of his stand in the society, people might not say much to his face but he would know that they wouldn't be extending the same courtesy won't be extended to Vidhi.
Forget ViDev for a second. If we randomly read some news article about a couple getting married with more than 2 decade age gap, most of us are cynical enough to say - he is that rich? / isn't he close to her dad's age than her own? That's the truth.
And whether it is this show or reality, there are bound to be issues even without the society interference. Tough ones which have the propensity and power to land deep cuts to one or both the partners involved. So it all boils down to how strong their feelings for each other are. And how determined they are to make it work. How much they trust each other's feelings. And most importantly, are they ready to keep ego out of their relationship completely.