it might be thanks to doctors who aggressively treat these older folks' health problems,

rather than taking an ageist approach that assumes they wouldn't benefit是定语从句吗

后面一句是定语从句吗

yes， exactly。“who aggressively treat these older folks' health problems。。。”是的，整体来修饰前面的these doctors。
可能得感谢这些医生们，他们积极地对待这些老年群体的健康问题的，而不是认为对他们没有好处而采取了歧视态度。

是， that后面作定语 再看看别人怎么说的。

eing conscious of health until we are ill.

肯定是定语从句。