Java Reflections - invoke method with BigInteger argument

I need to invoke methods in a class (called Foo in this example) using only Strings. For example passing BigInteger class as argument is not an option in my case.

My code works fine, when I use java.lang.String, but if try with other types, like BigInteger for example a "java.lang.IllegalArgumentException: argument type mismatch" is thrown

This is the class I am testing the reflection against:

package com.test;

import java.math.BigInteger;

public class Foo {

    private String name;

    private BigInteger age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public BigInteger getAge() {
        return age;
    }

    public void setAge(BigInteger age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Foo [name=" + name + ", age=" + age + "]";
    }
}

My goal is to invoke setAge(BigInteger age) method using Java reflections. This is the code I use:

package com.main;

import java.lang.reflect.Method;

public class Run {

    public static void main(String[] args) {
        try {
            Class clazz = Class.forName("com.test.Foo");
            Object obj = clazz.newInstance();
            Method m = clazz.getMethod("setAge", new Class[] 
{Class.forName("java.math.BigInteger")});
            m.invoke(obj, "12");
            System.out.println("after method call " + obj.toString());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Unfortunately after executing the code I get the java.lang.IllegalArgumentException.

To summarize my question: haw can I use arguments different than Strings using java reflections, given the type itself should be provided as String?