Is a high metabolism diet safe for a 90 years old men who want to lose weight? Thanks

Eat well. At 90, I'd say you can eat what you want. It's doubtful you need to lose weight. Generally, we recommend a balanced diet rich in fruits, vegetables. Lean protein and good fats should round it out. Your body will do the rest.
No. Not really: nutritional evaluation is imperative at this age, as is caloric intake, protein intake, fluid intake and vitamin supplementation are quite important.