When a night in sounds better to you than a night out. Also getting up two or three times a night for a pee. Getting up (eventually) and walking out the room only to forget why you did that.
My last 2 GPs have been significantly younger than me.
The thing that really gets to me is on social media when someone puts this album was released 30/35 years ago today and you remember buying it as a teenager. Most of my favourite thrash metal albums are heading fast towards the 40 year old mark