对typescript中这个复杂的'is not assignable to type‘错误的解释

interface Person {
  name: string;
  age: number;
}

function greet(person: Person) {
  console.log(`Hello, ${person.name}!`);
}

const user = { name: "Alice", age: "25" }; // age 是字符串类型，而不是数字类型

greet(user); // 这里会报错：Type '{ name: string; age: string; }' is not assignable to type 'Person'.

const user = { name: "Alice", age: 25 }; // 将 age 改为数字类型

const user = { name: "Alice", age: "25" as unknown as number }; // 使用类型断言

function isPerson(obj: any): obj is Person {
  return typeof obj.name === "string" && typeof obj.age === "number";
}

const user = { name: "Alice", age: "25" };

if (isPerson(user)) {
  greet(user); // 这里不会报错
} else {
  console.error("Invalid user object");
}