How you dress and carry yourself makes a big difference for sure, so make sure you are not overdressed and don't tell any "in the old days we used to do it this way" stories, or how far you are from retirement. Make sure they understand you are "all in" on the job and not just playing along because it is a convenient location or you need medical insurance etc. Definitely do NOT tell them what you told us, that you aren't really looking broadly and that you just thought this was a neat job ...
That's all I can help with. IMHO energetic old guys are a great addition to any team. I speak from when I was young.
G