Pruning is generally done with the purpose of producing larger fruit, and also to improve yield. Since old wood is less productive, that is what gets pruned out, even if it appears to be healthy. I prune our blueberry shrubs in February or March, before there are any leaves. I never remove more than 10% of the wood, but I am pretty conservative. You might have to take out more wood if the shrub has not been pruned in 10 years. I believe that "mummy berry" is a fungal disease that is carried from year to year in fruit that falls onto the ground below the shrub. It can be prevented by carefully raking up all of the dropped fruit, and removing it. Our shrubs get mulched with shredded maple tree leaves(Norway maple) and that seems to encourage the growth of compatible fungi, the kind that does not cause disease to the shrub or the fruit. There may be other mulches that have a similar effect.

In your situation I would wait for bud-swell to see where your flowers are. The flower buds are easy to differentiate from vegetative because they are much fatter.

The oldest wood will be easy to recognize before this but it will certainly help you decide how much to remove. The problem with not pruning for several seasons is younger, more productive wood can't get enough light to establish adequate flower buds or even stature so you may not want to remove all your old wood at once- just the wood without much potential the coming season.