If these MiG-29 are repaired and modernised they can be used for a long time. For example, Russia has new expensive Su-34 bomber. Yet, Russians use modernised old Su-24 that were designed and first built in late 70s. These old  modernised Su-24 bombers were quite effective in Syria.

As of now there are  4 MiG-29. 12 MiG -29 on order from Russia. 8 will be aquired from Belarus.

In addition old MiG-21 (20 machines) that were designed in late 50s.
And 17 Yugoslav built  Soko J-22 designed and first built in 70s. he rest are transport and trainer aircrafts.