If I may, on the age question, it's a very difficult question. It's certainly true that 16-year-olds get their supplies from 18-year-olds, so establishing an 18-year-old age limitation is going to increase use among younger people. It's also true that criminal records are catastrophic, but cannabis arrest is much more dangerous than most patterns of cannabis use.
Here is a possible compromise. In the U.S., states that vigorously enforce their law against direct sales from retailers to people under 21 experience reductions in alcohol use down the age range and in drunken driving down the age range, so that appears to be effective. That needn't be coupled with criminalization of possession or use by people under whatever the legal age is. If you enforce the law on the seller rather than criminalizing the buyer, I think you can get most of the benefit of the age restriction with relatively little of the cost.