Does metabolism slow down like that in your mid 20s?

Today I met an old friend of mine on the street, after 4 years. When I saw him I was shocked because he put on a lot of weight, when he was always skinny. Now he is 26.

I mean, the guy was always eating a lot but he had a very good metabolism and this was helping him keeping himself skinny. He was also a very active person. I don't know what changed in him. Maybe he got lazy and stopped being active? Or metabolism stopped working to his favor?

Oh Lord, I'm thankful I'm still skinny personally, although I never overeat. I always mind my quantities and I eat as much as I need to eat.
Does metabolism slow down like that in your mid 20s?
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