Average speed of a cyclist in the UK is around 9mph (we're excluding experienced/long term riders who can go much faster, here). Walking speed is 3mph, for reference.
Most cyclist deaths/head injuries are caused by collisions with cars hitting them, not the cyclist falling off and hitting something. If the car doesn't hit the cyclist, there's little to no risk to a rider that a pedestrian wouldn't be affected by as well.
As per licences, most cyclists have some form of experience/licence already and riding a bicycle really requires little skill to do. CPT's are encouraged in school, besides, most cycle and motorcycle training is learned by the rider themselves. Would 3 year olds need a licence to ride on pavements to ensure they don't hit other pedestrians? Is there a cut off age, but then what suggests a mature 13 year old is less capable than an ignorant 23 year old (or average deliveroo rider). You want MORE people on bikes not less. Creating barriers to what is an effective, cheap, healthy mode of transport means most wouldn't bother. The convenience and low cost of cycling is what attracts people to do it. We need a better infrastructure like Netherlands or Germany, not demonising cyclists because of poor driving habits that cause the incidents and bring it into question in the first place.