Contra Drum, Tyler Cowen is pessimistic: 

I don't see marijuana climbing the legalization hill, if it can't make it through current-day California. We're seeing the high water mark for pot, as aging demographics do not favor the idea. 

That assumes that today's younger anti-prohibition generation will get pro-prohibition as they age. But is that true? Maybe having kids changes things, but my experience of ageing boomers is that they're not anti-pot at all. Here's Ilya Somin on the question:

My tentative conclusion is that it's probably more of a generational effect. This is not just a difference between the very young and the rest. Rather, each successive age group is much more pro-legalization than those older than them. Even 50–64 year olds were 12 points more favorable to Prop 19 than the over-65s. Moreover, much social science data suggests that political attitudes tend to be fairly consistent with age, solidifying for most people when they are in their twenties. Winston Churchill notwithstanding, if you were a socialist at twenty, that implies a high probability you will still be one at forty. In addition, an important recent study suggests that the elderly actually become more socially liberal as they age, not less so.