You ask hard questions, @anna_5588! 
I wish I had a good answer, but… Practice. I have 40+ years of experience in doing things I don’t want to do.
I’m not trying to be glib, and I offer this response only as a possible explanation for me and my behavior, but I gave this some honest thought during my walk this morning and that’s the best I could come up with: My daily life is full of things I don’t want to do but do anyway, so I’ve become decent at “getting past” those feelings.
But that’s not to say age is a necessary condition. People a lot younger than me do amazing things everyday. (You, for the record, are one of those folks.) Again, I can only comment on my behavior, and so I suspect I’m better at this now than I was 1, 5, 10, 20, … years ago.
(Note also: Better, but not perfect. There’s plenty I don’t want to do and that I don’t actually do. But you only get a glimpse into maybe 2 hours of the 24 I live each day, so don’t assume I’m some sort of “model citizen” in this regard. I’m just some dude trying to do right by the people in my life.)