I think just being an adult. My kids play rugby on saturdays, things in my house break at inconvenient times, my son is now allowed to stay up late 2 days of the week. I need to read difficult books in the evenings. I have to get up early to accomplish everything. I have to do my taxes, vote, etc.
But also getting older means I won't live forever, and there is so much I want to do. I won't regret not watching TV, but I will regret never building a house, taking my kids backpacking, writing poetry, etc