If a startup is not making serious money after 2 years, it's probably dead in the water.
I don't think the time spent on a startup is a good measure of whether to give up or not. There are plenty of examples of companies that took longer than 2 years to get to significant revenue (and plenty more that have never turned a profit).
Is true about companies taking longer than 2 years to get significant revenue? I am in 20th month and barely hitting $5k per month with a burn rate higher than that.
Good to know other companies taking longer to get revenues; I don't feel like that much of a loser now ;)