Actually, it doesn't even have to be an actual grandpa. The elderly gentleman just has to look like a grandpa. That means he needs a kindly smile, a smattering of grey hair and maybe even a pair of glasses.
When Sadie sees a grandpa-looking-fellow, she goes crazy. She starts by cooing sweetly and then lets out a squeal of glee. She smiles her best little baby smile and leans in their direction. If she's having an especially coordinated day she will even wave her little hand. She may even lean towards them and try for a kiss.
It happened tonight at dinner at the restaurant at the golf course (she nearly fell out of her high chair leaning towards the man at the table next to us... although she also lavished her little baby attentions on Gigi, her actual great grandpa). She also chatted away with a grey haired man holding a carrot cake in the line in Costco yesterday (moments later she leaned over backwards and tried to kiss the young man who was getting the food ready to be scanned, on the cheek). It's hilarious to watch.
When Sadie was very very little, Paul used to say that he thought she was a little shy... I think we have all been disabused of that notion. It turned out to be just wishful thinking.
Sadie is a social butterfly. And a flirt!