Totally possible to have visible abs in your 30s and 40s, and even 50's. I'm only in my 30's but I've seen guys in their mid-50's with 6 packs. (They are fairly normal guys that run, not weird gym rats).
It sounds like you are, and probably always have been very skinny.
1. Having amazing looking 6-pack abs is a temporary phenomenon. Actors and models that you see pictures of probably didn't eat for a day beforehand and did an intense cut leading to the day they were going to have their picture taken.
2. Most people's problem is that they never get their body fat low enough. They probably have abs that would be visible but never lose the belly fat. That is less likely to be the case for runners and skinny people.
3. It seems like your problem is that your ab muscles aren't big enough or very well developed. I assume that you don't really do core work. Is this correct? It's easy to skip. I don't think you need to do this for an hour a day though. I bet that if you actually do core work consistently (10-15 minutes every other day) you will end up with a visible 6 pack. I bet that you notice results in the first two weeks.