You may be sensible and mature and just limit yourself to a glass of wine, but law states you cannot buy a drink until you are 18.
You may be sensible and mature and use precautions, but law states you cannot have sex until you are 16.
You may be able to swim 5,000 metres but you can't go in a pool at 7 without an adult, you may sink like a lead balloon but as long as you have had your 8 birthday you can go swimming on your own.
11 year olds are not allowed to leave a holiday care club unless they are signed out by an adult, but there is no law stopping that same 11 year old not being put in holiday care club and being left at home alone.
AIBU to think that some of the age laws are farcical (I haven't listed all the ones I disagree with here), but to have them while there is no law as to what age a child can be left at home (because parents are deemed in this one and only situation capable of knowing their own child) seems mad?