Years of experience
The sort of experience that IS valuable isn't so much to do with languages or technical skills. After all, languages come and go, development environments likewise and programming fashions, too. Plus, it's never too difficult to pick up the latest fad since there's very little that's actually new or novel in most of them. Added to which, most interviewers can't distinguish whether "6 years experience of XYZ" means 6 years of implementing new and ever-expanding techniques - or just 1 year of experience, repeated 5 times over.
The sort of experience that good people accumulate is knowing which of a list of requirements should be implemented first, which are difficult and which are wrong. Also being able to spot a project that's going off the rails (and knowing how to get it back - or whether to just let it go) and how to handle work issues like conflicting priorities, how to meet you targets and still keep your weekends free and how to tell the boss, in the nicest possible way, that he/she is a complete 'kwit and you're going to do the project YOUR way as that's the right way to do it.
The problem is that none of this is ever brought up at interview and is difficult to put into a CV in a way that a callow, just-appointed team leader, trying to recruit for the first time would recognise as a good thing.