The best time to raise money is when you don't need it. conversely, needing money to continue operating puts you and your company in a bad negotiating position with potential investors. Therefor i recommend if you can bootstrap do it, but have some clear deadlines/milestones in place to set expectations. things always take longer and cost more than you plan so discuss what happens when things don't go as planned. As you make progress make investor connections and keep them warm for if/when you need them. The more traction you get the more valuable your company becomes and the more options you have. Options are always good. If you can get to revenue and even cash positive while still bootstrapping all the better. At that point the market and competitors are likely starting to take notice and you may want to take outside investment for any number of reasons: to scale, to acquire competitors, allow founders to take some money off the table, etc. You never know what the market will do in the future so having cash in the bank to weather a recession, etc. is good if you can get it at the right price. I think the ideal scenario is: bootstrap your way to profitability, investors like what you are doing and approach you to invest, take some investment under good terms (for expansion, a war chest, and to reward your founders for some of their risk - this means investors agree that founders can repay themselves for foregone wages and/or sell some of their stock and put the cash in their pockets). This sort of scenario is not common, but not unheard of and i think entrepreneurs and their startups would be better off if they use this model as their standard. This sort of models helps startups to focus on being efficient.
regarding expectations for founders foregoing a salary: Everyone's financial situation is different so I would not necessarily make the assumption that co-founders over 25+ are in a position to forego a salary for 6-8 months. They may have the savings, but they may not have the risk tolerance or their spouse may not have the risk tolerance, etc. But if they are in a position to do so then that's a good acid test for their commitment to the project. An even better acid test is if they are willing to forego a salary AND put money into the company so you can spin up even faster.