It makes sense to avoid holding hands in public so as not to indicate whether a woman is a niddah or not. However, that is applicable to everyday life and not to a wedding. At a wedding the opposite is true. Most , if not all couples try to avoid a chuppas niddah and the assumption is that the kallah is never a niddah. If the choson does not hold her hand, the onlookers (and everyone is looking) may assume she is a niddah. Is that what we want? No, we want the opposite. So, hold her hand, it’s normal and desirable on all accounts.
In addition, a couple where the woman is in her fifties or older can never be in a state of niddah. Therefore, there should be no issue with an elderly couple holding hands in public. Besides, any male who is thinking about whether any woman of any age is a niddah or not needs psychological help.