How To Prune Black Currant

Our new black currant was picked up from the nursery and planted this year. It produced a small amount of fruit which have all been eaten by now, so I thought I would do some pruning to get more fruit next year. It turns out that black currant bushes produces the most fruit on 2 and 3 year old wood and this is only 1 year old. Pruning is done in December so I’ll have to wait. I’m supposed to keep 2 stems from each growing season and cut stems at ground level when they are older than 4 years. This picture shows what a bush should consist of, where a darker color means older wood. (A part of me wants to present this as a drawing done by our 1 year old daughter, but yes, I did it, okay?  ):

I know this is simplified but the goal is to cut stems that are older than 4 years in order to keep the bush young and producing the most fruit.

I don’t know why this pruning thing is so hard on my brain, so advice is always welcome.

Do you have experience pruning black currant?