There are many available birthday poems for a grandson, including "A Granny's Wish", "Eternal Bond", and "My Grandson is My Strength". There are some poems from the perspective of a grandmother, some from that of a grandfather, and others that could be from either or both.
More birthday poems from a grandparent to a grandson include "Love You, My Grandson", "My Lovely Grandson", "Proud Grandparents", "Thanks for Being in My Life, Grandson", and "To My Grandson". There are several websites online that provide birthday poems for grandsons and cover many different topics. A few other poems are "Your Smile is the Solution", "It Feels Just Like Yesterday", and "To My Dear Grandson".