I beleive the aircraft (serial no 22210 ) is actually 21 years old. Manufactured in 1984.
I have been flying this aircraft type for all of that time, including aircraft of the same vintage still flying today, and even on the same route.
No problem for the 757-200 although the payloads on that sector generate a lot of passenger baggage and general freight. As a result the 757 may prove to be volume limited after a short period of time. As I understand it this airlne intends to operate with 160 seats as opposed to a maximum of 235 seats so the additional luggage loads will be more than compensated for. The sheer volume of freight is likely to be a restriction eventually. My understanding is that the airline intends to add 767 equipment in due course and that will circumvent that potential difficulty.
Certainly the 757-200 is a very capable and reliable aircraft for building up that route, and likely to remain so within the companies route structure as it has a good deal of operating flexibility.
The 757 has been a reliable all rounder for many airliners for the last 20 + years with good payload / range flexibility. For specific markets and operations other aircraft types have been more economic in recent years, but many of those lack the same degree of flexibility where such a requirement is desired.