Eh, it's probably a choice.
When I was a teenager, my family lived next to an elderly woman in her early 70s. She was aged beyond her years because she had broken her hip in her 50s, and her doctor botched her surgery. She walked hunched over and in pain, but I never ever heard her complain. She rode a tricycle bike to get around (she didn't have a car), swam laps every day, attended college classes and corrected papers for correspondence courses (she was a writer). Even though she was 50+ years older than me, she would engage in teen talk ... listening to me gush about the guys I had crushes on, chatting about popular music and books. I honestly don't ever remember her talking about medications, ailments or doctors. As a teen, that would have been an instant turn off.
In contrast to my grandparents who complained about everything. And they wouldn't take advantage of their freedom in retirement to travel or do anything because they "didn't want to leave the house." They wanted to be there to protect it. I thought it was quite sad.
Even my mom is starting to sound "old" and she's only in her early 60s. Always complaining about her aches and pains, and saying she is "too old" to do anything that requires more effort than watching tv, other than for work.
If you don't want to be like your sister and BIL, then don't let yourself slip into the "old" mindset