My grandpa is really funny and sweet

I am 17. Sometimes he call himself my small baby brother and calls me his big brother because he is short. He is 5'3 and a half (161-162 cm) and I am 5'7 (170-171 cm). That time I adore him. And then the next minute he calls himself a big man and calls me a little newborn baby XD XD he is 66