Friends with a much older work colleague

I would just like some advice really.
Basically i have become good friends with a work colleague. She is actually old enough to be my mum (i am 32 and she is 65 next week). We are both female.
We had known each other at work for quite a while, and regularly had chats, sat on the same table in the canteen before our shift if we were on the same shift etc. But back in May we became good friends. We have met up for meals, gone out shopping etc.

But i am concerned of what other people at work may think. Even though we haven't actually done anything wrong, we are just friends, not hurting anybody etc, even though there is an age gap.
People may have already commented, i'm not sure. She actually finishes working there at the end of December. So there shouldn't be that problem after then.
But i'm just concerned about people at work gossiping and making comments about us being good mates.
And how is best to deal with it if it does occur?

I honestly don't see this as an issue at all - what kinds of things are you worried about them gossiping about?