But this has nothing to do with age. I believe it has to do more with drive. Or possibly intrigue.
Whatever the word you use, it is a problem of the mind.
The biggest thing I look in with my peers is their capability to push themselves, which also pushes the others around them. The former is a goal, the latter is a side-effect.
Reminds me so much of Hamming's You and Your Research: http://www.cs.virginia.edu/~robins/YouAndYourResearch.html
Oh, and yes, I'm in my early 30's and I suppose that makes me "Old", and I garner respect by the fact that I'm good at what I do and I tend to get shit right. But I also can act as a bridge between those who are younger and possibly less experienced (age != experience) and those who value age.
To be honest, I prefer to make a switch in "expertise" every five to seven years. This is a goal of mine to keep pushing myself otherwise I will get bored.
Languages learned between 30 and 40: Assembler, Pascal, C, C++, Perl, PL/SQL, T-SQL.
Languages learned between 40 and 50: Python
Languages learned since 50: PHP. (OK, I'm slowing down...)
Am I an expert in all of the above? No. Have I done very useful things with some of them? Yes.
You can be quite advanced in that particular skill if you practice enough for a long time. I picked up guitar when I was 27 when I started taking classes. Then it is up to your level of interest and commitment to reach a certain level.
'Expert' is up to interpretation. I'm only as expert as the other person who know and have practised less. When you think you've arrived at Expert level, you will stop advancing as much.
The trick is not to rely too much on experience and learn very quickly when the ground has shifted, and adjust your knowledge accordingly. I've seen many a peer fall over on the insistence that their experience is the only point of view when in fact technology or techniques have moved on.