My youngest grandson isn't physically demonstrative but is a warm and caring little boy. He is a quiet thoughtful boy, self contained, a little shy outside the family but a strong, happy personality. Now he is at school, [a big boy], what makes me smile is how he sits next to me on a sofa and ends up closer and closer until he is pushing right into me. This is permission for me to put my arm around him. Other times he comes over to talk to me and leans against me so we are physically close. He also likes to wrestle so there is a lot of contact and touch between us. It's very sweet. But cuddle and kiss? He is self conscious and uncomfortable now though [especially if someone is watching]. It's about what is comfortable to him, his body, his boundaries.
This is what happens OP when the grandchildren grow up. They form their own opinions and what they feel ok about and what they don't. They are individuals with their thoughts and feelings and needs not puppets or cuddly toys to make you feel better/fill you needs. He is telling you who he is...listen.
It changes as the years go by and you need to curb your hysteria and self entitlement/ownership of him as there are going to be many more phases, changes and periods of growth in front of you both. [Especially when 13-14, in my experience for example. Be prepared].