Once you become an adult with a job and bills and maybe other people sucking at your literal or metaphorical teat for sustenance, your birthday stops becoming a big deal. Or it should stop becoming a big deal, unless you’re some sort of ego maniac who has to tell strangers at the grocery store, “Hey, see this cake I’m having frosted? It’s for me because it’s my birthday! What did you get me, stranger???”
Then, if you live long enough, your birthday becomes a big deal again, just by virtue of the fact that you’ve been around a really long time. Your superannuated existence becomes an excuse for people to get together for a big party and outdo each other giving you lavish gifts. This goes on for a while until you either die or become so old that a big birthday party with fancy gifts and mountains of cake just isn’t enough anymore. You have to do something really big because you’re not just a regular old person — you’re the old person, the oldest, wisest human in your zip code, at least. So you do like Dorothy Custer did on her 102nd birthday and go base jumping while strapped to a handsome young man because life’s too short to pretend you like the shitty sweater your grandson bought you just so he could feel better about mooching your cake.