How old is to old to be in diapers and using sippy cup?

I have a friend that has a 3 year old, that still in diapers and she still gives her a sippy cup. She thinks I'm crazy when I tell her that her daughter is to old for both of these.

    There comes a time in everybody's life when you're too old for something, and I think this little girl is manipulating her mother. My oldest wasn't completely potty trained till he was 3-1/2, but that was my fault. I worked full time and was unsure how to go about potty training. My other three were potty trained before 2-1/2.
    About Vickie
    Birth: December 31
    On since: Feb 10, 2016
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