They're not making cigarettes or smoking illegal, just the sale of tobacco to certain people. People born before 2000 will be able to carry on buying it for their younger friends, so there isn't a direct comparison with other drugs.
In 70 years time you may well find 80 year olds hanging around outside newsagents hassling 90 year olds..'oi mister, buy us some cigs. Here's £200 for twenty bensons'...or maybe not, because by then the practice will be pretty much obsolete because of all the other factors like cost, education, and the effect of the law itself in preventing people starting to smoke.
It's an interesting idea.