Yes, big bdays are important, The same is true for the very young too, e.g., 1 yo is a big birthday for a grandson/granddaughter (but its significance is likely to a less degree than older parents’ big bdays.)
“Meet SO” is usually followed by a wedding, which is eventually followed by producing the grandchildren. So hopefully we are not off track too much. (Isn’t it true that many CC parents generally love any topics remotely related to the wedding?)