Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
|  | Average  Seating Capacity | Average Age (Years) | Owned | Leased | Total |
| --- | --- | --- | --- | --- | --- |
| Airbus A319 | 128 | 13.8 | 21 | 104 | 125 |
| Airbus A320 | 150 | 16.7 | 10 | 38 | 48 |
| Airbus A321 | 178 | 5.4 | 165 | 54 | 219 |
| Airbus A330-200 | 251 | 6.0 | 15 | — | 15 |
| Airbus A330-300 | 291 | 17.4 | 4 | 5 | 9 |
| Boeing 737-800 | 160 | 8.1 | 132 | 172 | 304 |
| Boeing 737-8 MAX | 172 | 0.1 | 4 | — | 4 |
| Boeing 757-200 | 180 | 18.1 | 31 | 3 | 34 |
| Boeing 767-300ER | 209 | 19.1 | 24 | — | 24 |
| Boeing 777-200ER | 269 | 17.0 | 44 | 3 | 47 |
| Boeing 777-300ER | 310 | 3.8 | 18 | 2 | 20 |
| Boeing 787-8 | 226 | 2.1 | 20 | — | 20 |
| Boeing 787-9 | 285 | 0.7 | 14 | — | 14 |
| Embraer 190 | 99 | 10.2 | 20 | — | 20 |
| McDonnell Douglas MD-80 | 140 | 21.3 | 13 | 32 | 45 |
| Total |  | 10.1 | 535 | 413 | 948 |
Question:
On average how old were the Airbus A321 fleet for American Airlines in 2017?
Answer:
5.4