By old gun I mean something that you picked up 10 - 15+ years ago and it is still your primary or only EDC. Have you modified it? Have you dragged it kicking and screaming into the 21st century so that you can keep your old-school auto or wheelgun but have added a light or red dot when it wasn't designed for it?
I have several "primarily" EDCs. I carry something different depending on what I'm wearing and where I'm going. I own all the new toys like the Hellcat, Shield Plus, Glocks, M&P 2.0, CZs, Sigs, you name it, but I perfer older tried and true firearms. I don't really carry any of the my newer higher capacity, flavor of the month, latest and greatest firearms.
To your second question, It's my personal opinion that it's sacrilege to put lights, lasers, or optics on classy old school metal frame pistols and revolvers. I relegate that stuff for my polymer crap.
It's still relevant and sold today, but my Ruger LCR 357. It gets carried often as a primarily in my pocket or as a BUG. Purchased it back in 2012, so it's going on 12+ years now. It's the first revolver I ever purchased, but now I own about a dozen.
Now Discontinued by Kahr, my MK40. It's over 24 years old. I will typically carry it OWB concealed with only a t-shirt on in the warmer months or when I need extra concealment. It's kinda sorta been replaced by my Springfield Hellcat, but still carry it.
I've been carrying this the most lately. It's my Kahr K40 from early 2014, so it's over 10 years old. It's been discontinued too.