Why do women who are older than me suggest that I'll become fat?

Women have been telling me since I was 16 that once I reach 20 my metabolism will slow and I will have to bust my butt in the gym just to stay at a decent size.

I'm quite a bit over 20 now and I still have abs and I hardly spend any time in the gym or working out. My diet is pretty much the same as it was when I was (which wasn't that bad to begin with). I love pizza and french fries and I still eat greasy stuff like that like once a week.

Women are still telling me that I'll become fat. Why do they say this?

Updates
+1 y
*the same as it was when I was 16
Updates
+1 y
So everyone eventually becomes fat

LOL
Why do women who are older than me suggest that I'll become fat?
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