How to provide feedback or gauge colleague?

If your company has a rubric of what success looks like at each level, you can point your mentee to that. Then, you can draw a line between their current behaviors and the behaviors at the level where they want to be and see whether they are falling behind or exceeding the expectations.

If they are junior, the goal for them is mainly to become more independent where they go from require a lot of hand holding to almost no hand holding.

I like this question alongside your passion to deliver good feedback to people - That's a good instinct!

How do we gauge colleague over time to provide constructive feedback?

Just be observant and see if they mess up with anything. A very easy way to make this very concrete is to think to yourself "What would I do in their situation if I was them?". Would you have:

• Written their commit the same way?
• Spoken the same way in the team meeting?
• Prioritized the same tasks they did?

If there's a difference (there probably will be), ask yourself if the difference made sense of it's because the junior engineer doesn't know what they're doing yet and can definitely improve.

What expectations should we set for new joiners when they ask about career progression?

This isn't a question for you as a mid-level engineer and is much better suited for the manager. Different companies have different cultures around promotion and different average promotion speeds. For example, I could confidently tell new grad mentees at Meta that they could grow fast if they implemented my advice and performed well overall (up-or-out is a forcing function too). At PayPal, I would effectively tell them 🤷

Lastly, I highly recommend going through our junior to mid-level course: Grow From Junior To Mid-Level Engineer: L3 To L4

It provides a very clear picture and roadmap for juniors to grow to the next level. Use that as an anchor to give them feedback to grow.