Translate the following question to SQL: Who has friends that are younger than the average age?

Schema: CREATE TABLE Person (
    name varchar(20)   PRIMARY KEY,
    age INTEGER,
    city TEXT,
    gender TEXT,
    job TEXT,
    UNIQUE (name)
);

CREATE TABLE PersonFriend (
    name varchar(20),
    friend varchar(20),
    year INTEGER,
    FOREIGN KEY (friend) REFERENCES Person(name),
    FOREIGN KEY (name) REFERENCES Person(name)
);
user
SELECT DISTINCT T2.name FROM Person AS T1 JOIN PersonFriend AS T2 ON T1.name  =  T2.friend WHERE T1.age  <  (SELECT avg(age) FROM person)
assistant