Virgin Australia has taken care of long-term fleet replacement with an order for 23 Boeing 737 MAX aircraft, and at the same time the carrier is reshuffling its medium-term fleet plans.

The 737 MAX 8s are due to be delivered between 2019 and 2021, and are intended to replace the airline’s oldest 737-800s rather than growing the fleet, a Virgin Australia spokeswoman tells Aviation Week.

The carrier currently operates 62 737-800s, many of which are new deliveries that began arriving in May last year at the rate of about one per month. Virgin Australia also has seven 737-700s in its narrow body fleet, but these will be gone by the end of 2013.

Virgin Australia also announced it will be deferring an undisclosed number of the 737-800s that it has on order. Under its revised plan, it will take delivery of 31 -800s between 2013 and 2016.

The reason behind the deferrals is to give the airline more flexibility in the medium term, the spokeswoman says. In a statement, the airline says this flexibility will allow it to “develop the appropriate mix of narrow-body and wide-body aircraft.” Virgin Australia’s fleet is heavily dominated by narrow bodies, so it may be signaling that a wide body order is coming. The airline’s wide body fleet includes five Airbus A330-200s and five Boeing 777-300ERs.

CEO John Borghetti says Virgin Australia has reduced its average fleet age to 4.2 years over the past year, down from 4.9 years. He says the carrier “will continue to review its fleet strategy to ensure we align fit-for-purpose aircraft to markets and maintain maximum flexibility in capacity management.”