Can I get admission in B.Tech lateral entry even after having a gap of 2-years after completing Diploma in civil engineering?

Yes, you can take admission, but you have to show a graph certificate for 2 years. And, after that an examination is conduced called LEET. And, on the basis of that rank, you can get the admission.

Some colleges do have an age limit. You will have to check for that. You can present an affidavit at the time of admission that states the reason for your gap and you will be able to take admission.