Do you think there should be an upper age limit on voting?

Here in America, The Democrats were grabbing at straws recently with a 16 y/o voting age suggestion. That said...you can't drink until you're 18 or older in many states, most likely need a driver's permit at 16, though no military draft in place, we probably would not draft 16 year olds. With the gun issue ages have increased to above 18 to 21 or older, but they wanted, not quite fully educated (and that's not a slight at 16 y/o) to vote. Those at the end of their spectrum as you say, either have voted and contributed to their country, and should not be denied the right to vote. As for consequences, those who are the generations behind them at the current age(s) to allow voting if they chose to do so, could reverse the consequences you mention (in your case Brexit)