如何使用 unknown 检查对象类型?

```
function check(v: unknown): v is { name: string; age: number } {
if (typeof v !== 'object' || v === null) {
return false;
}
const a = v as { name: unknown; age: unknown };
if (typeof a.name !== 'string' || typeof a.age !== "number") {
return false;
}
return true;
}
```

其中 `const a = v as { name: unknown; age: unknown }` 比较丑, 怎么写才好?