I think the lack of explicit programs is because the path is often "stick around long enough to have enough things you can point to that look similar in complex

I think the lack of explicit programs is because the path is often "stick around long enough to have enough things you can point to that look similar in complexity / effort as other things people with the Senior title have done." If all those things require relatively little hand-holding then the solution is just progressively less and less hand-holding, often in the form of "toss them in the deep end and only go hold their hand once they ask for it". That has some negative incentive structure of course, but so do other suggestions proposed here... Maybe instead focus the mentoring on becoming a better dev. Have them join your book club (or paper club, talk club, blog club, whatever) that you in theory already have going on where engineers at whatever levels get together and discuss a topic and how it can be applied to make them better engineers or have better team dynamics etc. Maybe do some applying exercises / experiments too. The "junior" and "senior" distinction isn't very important beyond salary negotiation, and often the "needs guidance to excel" or "not fairly independent yet" criteria can be misleading too because it's somewhat sensitive to the work and work environment in question. If you really want to mentor a junior into a senior you just need to make them more like the what-does-this-company-mean-by-senior person, which might not correlate very well with good engineering at all and can differ quite dramatically from company to company.