Absolutely. Startups should not hire junior engineers. They don't have time to teach people until they are a functioning profitable business.

However, I would not encourage learning at an agency or consulting service. The best place to learn by far is at a large corporate company, where you have the time to learn good programming practices, and people to teach you how to do it well. The problem with consulting is that you're always working on a short-term issue, and never learn the value of writing good code for long-term support.