So bittersweet watching your youngest start to pass milestones your older child hasn't met

My 7 month old is starting to wave and I'm so excited for him, but at the same time it makes me so sad because my 2.5 year old still doesn't understand the concept of most gestures (waving being one of them). I feel bad for not being able to fully enjoy my baby hitting a milestone. Even worse, I know this is just the beginning of a series of milestones I won't be able to fully enjoy because I feel bad that he's surpassing his older brother in certain areas.

(Just venting, do not need support but there's no tag for venting without needing support)