Goals need to be appropriate to the timescale and skill level of the mentee. Setting goals that ask far too much of them can cause them to lose heart as they repeatedly fail to meet demands.
On the other hand, easily attainable objectives do little to promote growth. Both parties should work together to formulate goals that stretch the mentee’s abilities and push them to achieve more than they thought possible while simultaneously keeping them realistic.
For example, it would be challenging but realistic to expect that your mentee gets certified in a critical piece of software within three months. It would be unachievable to think they could be a subject matter expert in that same time frame.