I finally came across Scripture that explains why we gain weight as we get older. The struggle is real but even the Bible says...

Psalms 92 (KJV)

¹³ Those that be planted 

in the house of the LORD 

shall flourish in the courts of our God.

¹⁴ They shall still bring forth fruit 

IN OLD AGE; 

THEY SHALL BE FAT AND FLOURISHING;