I promoted someone to warehouse manager at 24 who everyone thought was too young. He'd been with us eight months. Best decision I made that year, and here's why: he'd already started solving problems I didn't know we had.
The signal wasn't tenure or technical skill. It was ownership without permission. This guy noticed our receiving team was getting slammed every Tuesday because certain brands shipped their weekly inventory on the same day. He mapped it out, called three of our clients directly, and convinced two to shift their delivery window. Our Tuesday bottleneck disappeared. I found out about it two weeks later when I asked why receiving looked so smooth.
That's the milestone I look for: when someone starts managing up instead of waiting for direction. They bring solutions, not problems. They've already built relationships across departments. Most importantly, they're making your job easier without you asking them to.
Here's my actual promotion test at the fulfillment company. I'd give a high-potential person a contained project with real consequences. Not busy work. Something like: we're adding a new client with specific temperature requirements, figure out what equipment we need and build the onboarding process. Then I'd watch how they handled ambiguity. Did they ask me to solve every decision or did they research, propose options, and own the outcome? The ones who came back with a full plan and said "here's what I recommend and why" got promoted. The ones who kept asking "what should I do next" needed more time.
The mistake most founders make is promoting based on performance in the current role. Your best picker might be a terrible pick supervisor. I learned to separate execution skills from leadership capacity. Can they teach someone else to do their job? Have they already started doing it informally? When they're on vacation, does their area fall apart or keep running?
One practice that saved us: I made every manager-track person run our weekly all-hands meeting at least once. You learn instantly who can command a room, synthesize information, and make fifty people care about the same goal. It's a low-risk audition for the real thing.
The best operators don't wait for a title to start leading.