Zwit,
When the ex RAF aircraft came onto the Civil Reg there was a mixed bag of airframe life's. Not all were of a high F.I. Much is misunderstood about the Bulldog F.I life. In essence if you have a fatigue meter fitted then you can fly the aircraft until F.I 114.0. At that point you would need to get a spar mod done.
If you are thinking about buying and ex Swedish Airforce SK61 Bulldog that has not had a fatigue meter fitted then you have up to 5,000 hrs total airframe time before the aircraft is out of life.
In 'normal' ownership doing G.H, occasional 'gentleman's aeros' and moderate circuits I would think you will be doing around 0.6 F.I per year. In service this figure was higher simply due to the amount they were flown and more aero sorties.
Picking up a nice aircraft does take time and suggest calling De Havilland Support at Duxford if you want help with a pre purchase inspection.
Owning is not for the faint hearted, there are a lot of lifed parts that need replaced. That said they are still under valued and you have to think what else you can buy that's as capable for that money.
All the best
Big Sand