My elder son has gone quiet since his baby brother arrived. Or is it just the age?

Our elder son used to tell us everything about his day, whether we asked or not. Over the past year it has become 'okay', 'nothing much' and 'can I go now'. The baby is nearly one and naturally takes a lot of our attention, so I keep wondering if that is the reason. He is lovely with his brother, makes him laugh, never complains about him. That almost makes it harder to read. How did you tell whether it was the new sibling or simply the age? And does the talking come back? ❤