How long can my health last?

Man, I deeply resonate with your question. It's not really asking "how long can I live?", but rather "how long can my health endure under this kind of work state?"

I can't claim to give you a standard answer, but as someone who's probably experienced this earlier than you, I'd like to share my thoughts.

Health isn't an HP bar; it's a "resource pack".

Don't imagine health as a game's health bar, where you lose a bit when hit and it's Game Over when it's depleted. It's more like the "initial capital" and "cash flow" in your startup project.

Initial Capital (Physical Foundation): What your parents gave you when you were young; some have more, some less. You're young, so you might feel like you have plenty of capital, pulling a few all-nighters and still being able to keep going with a cup of coffee the next day.
Cash Flow (Daily Consumption & Replenishment): This is the key. Your daily work, stress, late nights, and irregular meals are all "expending" your health. Meanwhile, rest, exercise, eating well, and relaxing your mind are all "depositing" into your health.

Your question "how long can I last" depends on whether your "cash flow" is positive or negative.

If your daily consumption far outweighs your replenishment, then no matter how robust your initial capital, there will always be a day of "bankruptcy". This "bankruptcy" won't be sudden death (though extreme cases do happen), but will manifest in various forms:

'Minor Ailments' Stage: Neck pain, herniated discs, insomnia, stomach aches, severe acne, hair loss. This is your body giving you a "yellow card warning", telling you there's a cash flow problem. Most IT engineers and entrepreneurs are in this stage.
'System Warning' Stage: Your immunity plummets; you used to catch a cold once a year, now it's once a month, and each time it drags on. Signs of the "three highs" (high blood pressure, high blood lipids, high blood sugar) appear. This is your server starting to report "Critical Errors"; if not dealt with, it will crash.
'Major Failure' Stage: More serious organic lesions appear. This is like your hard drive crashing, data lost, and recovery becomes difficult.

So, how can this "company" avoid bankruptcy and last longer?

Simply put, it's about "increasing input and reducing output" (in terms of health). Don't expect to become a fitness fanatic overnight; that's unrealistic. Start with the Minimum Viable Product (MVP) you can achieve:

Force yourself to 'clock out': Entrepreneurship might not have a concept of 'quitting time', but your body needs one. Even if it's just absolutely no work discussions after 11 PM, watch a show, read a book, let your brain switch modes. This is "clearing your memory".
Treat exercise as a 'check-in task': You have task lists for coding; health needs one too. No need for a gym; just start with 10 minutes of standing and moving around daily. Use the Pomodoro Technique: every 25 minutes, get up to grab water, use the restroom, or look out the window. Or, turn meetings with co-founders into walking discussions.
Don't just 'make do' with meals: Takeout is inevitable, but you can consciously order more vegetables and less oily/salty food. Ensure at least one meal a day is eaten mindfully. This is like upgrading your server's power supply; it adds a lot of stability.
Invest in your 'workstation': Get a better ergonomic chair, a monitor stand, and if possible, a standing desk. This small investment is a drop in the ocean compared to future medical bills for neck and back issues. This is upgrading your "hardware".
Find your 'mental anchor': Entrepreneurship is stressful; you need an outlet. Playing games, watching movies, spending time with family, petting cats or dogs – anything works. Don't shoulder all the pressure yourself, or your mind will break before your body does.

In short: Don't worry about 'how long you can last'; worry about 'what more can I do for my health starting today'.

Your career is a marathon, not a sprint. If the '1' (your body) collapses, all the '0's (achievements) that follow become meaningless. Manage it as your most important project, allocate time and resources to it, and it will accompany you until the day you ring the bell.