This would definitely be considered age discrimination. It shifts the balance of power towards the young. And because the young vote less often, it would shift towards a smaller portion of the overall population.
You identify the one significant pro. It would shift the power towards those who might be affected the longest time.
The accompanying con though is that there is already a way for the young to address that. They will only be young and outvoted by the old for a limited time. Eventually the old will die or at least become sick enough to no longer vote. So the young can then win those votes and change the law. Until they do so, then the young and old should share that responsibility. The old have just as much right to control the next year of their life as the young do. Once the old are no longer there, the now older but previously young can step forward and join with the even younger for a new result.
There is also the problem of the young having less life experience. I.e. many people look back on decisions they made when young and think about how they wouldn't do that again. This gives more power to the people with the least ability to aim it.
Under this logic, shouldn't the unborn get the greatest influence? They will be impacted more than anyone living, as they have a longer life expectancy. And there are so many of them. You can go forward an arbitrary period of time so as to have more unborn people than living people.