Ask HN: How can one continue to grow after reaching the top?

I'm one of the 3 most senior team members where I work. Working with these colleagues has helped a lot with grow my skills, simply through discussions, and other normal work interactions. From their feedback I'm convinced this goes both ways.

Recently, a friend of min asked (read: begged) me to come working at his company, in a kind of CTO-like position. I've done odd jobs for this company, and like working there very much (they have fostered a great atmosphere). Due to the nature of the company, most of the employees are unskilled laborers. The tech team currently consists of 2 college students and the aforementiond friend, a CEO with only limited tech experience. I get to stipulate the terms of me working there, so I could probably add a few team members, but it's not likely I'll get to add any seniors to the team, as those are hard to find, and may not be in the budget.

I've learned that growth is very important to me, and in the past I've always grown by working with people with more or equal experience. If I take this job, that style of growth will no longer be available to me. How do other HN-ers improve their tech skills, when they are not surrounded by experienced collegaues?

TLDR; I'm about to reach the top, and I don't know how to grow from there.