I agree that there's a hint of ageism there in the standard case (i.e. the one you describe), and that's likely due to seeing someone w/ 15 years of experience

I agree that there's a hint of ageism there in the standard case (i.e. the one you describe), and that's likely due to seeing someone w/ 15 years of experience in Java registers (perhaps subconsciously) as "old guy". And indeed, being young was how I fell into my first radical shift around 2000, from C based systems level stuff to R based bioinformatics tools. And admittedly, despite what I said previously I also hold it against people at times if all they've worked with is a single technology and they've done it for a very long time. To me that shows a potential lack of flexibility and perhaps they might not be able to transition to new technology all that easily. Even if a company thinks their stack is stable, it might change at any point and IMO it's good to have someone who can pivot easily. Also, as I mentioned previously having that broader range of experience is useful in terms of spotting pitfalls or good approaches.