Translate the following question to SQL: What is the average and minimum age of all artists from United States.

Schema: CREATE TABLE artist (
    Artist_ID INT   PRIMARY KEY,
    Name TEXT,
    Country TEXT,
    Year_Join INT,
    Age INT,
    UNIQUE (Artist_ID)
);

CREATE TABLE exhibition (
    Exhibition_ID INT   PRIMARY KEY,
    Year INT,
    Theme TEXT,
    Artist_ID INT,
    Ticket_Price REAL,
    UNIQUE (Exhibition_ID),
    FOREIGN KEY (Artist_ID) REFERENCES artist(Artist_ID)
);

CREATE TABLE exhibition_record (
    Exhibition_ID INT   PRIMARY KEY,
    Date TEXT   PRIMARY KEY,
    Attendance INT,
    PRIMARY KEY (Exhibition_ID, Date),
    UNIQUE (Exhibition_ID, Date),
    FOREIGN KEY (Exhibition_ID) REFERENCES exhibition(Exhibition_ID)
);
user
SELECT avg(age) ,  min(age) FROM artist WHERE country  =  'United States'
assistant