I'm over 40 too, so I say this from personal experience: the body tightens faster and recovers slower. It's not a reason to stop moving. It's a reason to move smarter.
Mobility is about more than flexibility. It's about control: being able to move into a range and actually do something there. Yoga builds that. Each pose teaches you where you're holding tension, where you've lost range, and where you can recover it with patience.
Consistent practice twice a week makes a noticeable difference within a few months. Not just on the mat. In how you wake up in the morning, how you sit, how you carry yourself through the day.
Pose to try
Pigeon Pose (Eka Pada Rajakapotasana)
Bring one shin forward on the mat, extend the other leg back, and fold slowly over your front leg. The hips are where most of us carry the most tension, and Pigeon goes straight there. Hold for at least a minute on each side and breathe. Don't rush it.