What's wrong here using 'Object' as a substitute for specific type?

Question

I wrote some code to test Supplier and something went wrong but I don't know why.
here is the code:

import java.util.List;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class Client {
    public static void main(String[] args) {
        List<Integer> list = IntStream.range(1, 11).boxed().collect(Collectors.toList());
        List<User> newList = addToList(list, User::new);
        System.out.println(newList);
    }

    private static <T extends User> List<T> addToList(List<Object> srcList, Supplier<T> sp) {
        if (srcList == null || srcList.isEmpty())
            return null;
        return srcList.stream().map(src -> {
            T t = sp.get();
            t.setAge(Integer.parseInt(src.toString()));
            return t;
        }).collect(Collectors.toList());
    }

    static class User {
        Integer age;

        public Integer getAge() {
            return age;
        }

        void setAge(Integer age) {
            this.age = age;
        }
    }
}

List<User> newList = addToList(list, User::new) it has an error here says:
"Bad return type in method reference: cannot convert User to T".
Then I change the private method to below:

    private static <T extends User, R> List<T> addToList(List<R> srcList, Supplier<T> sp) {
        if (srcList == null || srcList.isEmpty())
            return null;
        return srcList.stream().map(src -> {
            T t = sp.get();
            t.setAge(Integer.parseInt(src.toString()));
            return t;
        }).collect(Collectors.toList());
    }

and there is no error this time.
What's happened here? Every class should be the subclass of Object, buy why can't I use 'Object' here?
I would appreciate it if someone help me.