Lovelee, anyone can refuse to be interviewed. Its even written into the caution given on arrest.
"You do not have to say anything unless you wish, but what you say may be given in evidence"
The longer formal caution is given when charged, but the substance is the same.
Basically, the Police have to assemble enough evidence from complainants and witnesses to convict him in the absence of an interview and confession.
Another thing, if he is senile, or otherwise incapable, its pointless taking him to court - the defendant has to understand whats going on.