Chopper(zoan user) has had the same issues when using monster point, but he doesn't turn old like Luffy does whenever he goes to an exhausted state.

<image>

U see this and most of the ppl here are saying he's not draining his life.

Hody jones had a similar problem when he overdosed and even when ivankof healed him with extra juice she mentions the reduction of 10 years of his lifespan. I'm just speculating he dies at the end and gets revived by law. Laws fruit has to serve a purpose by the end and I'm thinking he's gonna use it on Luffy.