My female betta is acting different lately she is slower?

Ive had this female betta for 1 year and a half and when i got her she was soo tiny and so white she was almost see through. Now she's dark blue but lately she's been different maybe it's been happening longer but i just realized that she settles down a lot on the bottom of the tank. When she swims she mostly swims with the front of her body aiming up as if her backside was heavier. She doesn't swim around as much. Is she getting old already? I mean it must be that because i only feed her once a day at night and not twice like it says in the bottle, she is big or bigger but what can it most likely be? How long do bettas live anyway??