I get that it's more difficult to do such changes the older you get just from a psychological standpoint, especially if your body is used to a caloric surplus (

I get that it's more difficult to do such changes the older you get just from a psychological standpoint, especially if your body is used to a caloric surplus (which it probably is if you're thinking about going to a 500 kcal deficit). But I'm interested in knowing if the body metabolism really changes so drastically when you get older as to make a -500 kcal diet impractical, and where the cutoff for practicality would then be.