Nonprofits may spend as much or as little as they like on admin. costs, though they may be flagged by the IRS for spending a huge amount on admin costs for several years, which may result in an audit. It is pretty typical for a new nonprofit to spend more $s on admin as they get the nonprofit up and running.
Salaries are not considered across the board to be an administrative cost. If a staff person is working on programming, then this is a program cost, not admin. When I was the ED of a nonprofit, 80% of my time was spent on programming and 20% was on G&O, and our financials and 990s reflected that (I had to detail what I did with my time for the auditors to come up with that ratio).
ETA: these were our internal auditors, not from the IRS