But so what? You're enjoying it, and from the sounds of it you're probably making enough that nobody involved is going to starve or end up buried under a debt mountain. Managing the downside risk works out to "use a lawyer and don't sign anything with stupid terms."
As long as you're keeping your skills up, your failure mode is "quit, get a job somewhere playing code monkey for (floor $60k/yr, ceil ???)." You've got a safety net that is virtually unrivaled in history.
So go nuts, be young, spend a few years making mistakes and learning stuff. As career trajectories go, "failed startup" is far better for your resume than "agency seat filler" - at least for the next year or three, and assuming you do your due diligence with regard to skills maintenance, networking, and documenting your expertise (which would be equally important as an agency seat filler).
Yeah, there are better ways to optimize for career trajectory. If that's your sole priority, you should probably land a job at Googlesoft or in a field like finance, then spend the next year or three focused on networking your ass off.
But would you be happy with it, during or after? Probably less so.
Since neither option is exactly going to have you standing in the bread line, even if your choice of venture turns out to be a spectacular failure - you're free to choose based on personal fulfillment, not just socioeconomic leverage.
And, you know, it could work out. Which would be nice, but it's not something that's necessary for it to be worth your time.
