Yes you read correctly, I can't be arsed, and neither can DH. And yes I am sure we ARE 'only in our 50's.' So what? Not everyone is the bloody same you know! 
We have travelled extensively over the years, (to 50+ countries ...) and have had very busy and stressful professional jobs, that have taken us all over the world, and have been to multiple dozens of shows and musicals, in New York and London, and Paris, and other major cities. You name it, we have seen it.
We now live very rural, miles from anywhere, and couldn't be arsed with the ballache of going to a show 50-70 miles away now. (Especially when the train station is 20 miles away!) And I am pretty sure we are not the only ones who feel this way. Obviously loads of people will now appear on here telling me how they are 50, 60, 70, whatever, and they would LOVE to go and I am weird and so on...
But as I said, we have done it all. Maybe some people haven't done the things they wanted to earlier in their life, and want to do it all later on in life. Fine, but don't judge us for not wanting to bother, as we have already done everything we want/seen everything we want. After a very busy, hectic, professional life and career, both me AND my husband are now very happily retired, and like to live a very quiet life now, in our lovely country home, near the woodlands. And cannot be arsed with fuckall. That is our choice, so don't judge us because it's not YOURS! 
As I said, the OP needs to check her dad will want to go to a show Maybe he won't. Not EVERYONE is the same!