Mandatory firearm safety and proficiency training started in elementary schools. This must include rangetime and annual safety refreshers, qualification tests and regular, subsidized practice. Field trips to long range or IDPA facilities. Get kids started with airguns as soon as they're physically able. Destigmatize the possession and use of personal firearms for sport, defense, and other political reasons.
Encourage youth participation in the shooting sports. Get the NRAs head out of its rectum and back it its lane promoting the shooting sports- for example varsity skeet, rimfire benchrest and pistol.
And if that doesn't work, follow up with forced 24 month conscription for all able-bodied citizens between 17 and 19 years old without regard to race, economic status, or gender identfixation.
Edit- Holy horsefeathers. I've become an old man!