As per my earlier post which is buried on the end of the last page, it will be the expensive "D" checks that kill them off..... not specifically age.....
Remember EZY have parted out 6-7 year old NG 737s for spares because they were due a "D" check....
These aircraft will give BA some breathing space.......

I would not feel totally relaxed on a 737 that has spent its life with Garuda or air Vanuatu. ....