Your 100th birthday speech to grandfather needs to be really unique. It should cover the events of a long lifetime and speak of how much he is loved by family and friends. It’s definitely a time for looking back at his achievements. Our speeches say all these things and you can choose to use one or pick selected passages from the pack.
There are specific toasts with each 100th birthday speech to grandfather. You can end with one of those or with one of the short poems that are guaranteed to entertain and surprise the guests.