I don't think your age has much to do with it.
But why are we going into depth in this if you don't have the cash to buy one, let alone do the necessary repairs each and every e39 needs at given intervals (not cheap to run these, as pretty much all here will agree with)
Are you just short of the cash, or are you yet to start saving for this?
To add: I had never heard of the brand Holden Cruze so i looked them up. Apparantly the 1.8 is the standard engine which is sluggish and slow. They have a 'sports' version with a whopping 1.4 liter turbo engine that produces approximately 140hp and 200nm torque. Comparing this to the 231hp 530i with 300nm torque it really does prove that these 2 cannot be compared...Note the BMW only weighs 133 kg more