I took extra time to finish mine too. I just put the year I graduated on it and not how long it took. It's never come up and couldn't imagine it being an issue if it did.
A computer science degree is a serious challenge. There is no shame in taking longer than 4 years to finish it.
Luckily they did give me an offer for an internship. I thought it was probably a strange question to ask. It was in my third interview they asked, after I already passed the phone tech screen and programming challenge. Maybe they were already set on hiring me, and wanted to ensure I was drinking age?
I'd be far more concerned that you are so completely unaware that this info isn't even generally on anyone's resume...