I will be 40 this coming up november and I have a pretty decent 6 pack for an "old guy" haha. You can see a pic I took of myself as my avatar. The only problem I am having is lower ab skin that I have from being overweight periodically throughout my life. I am 6ft tall and currently around 218 pounds but I can easily go between 215 and 245 in a blink of an eye. It's all about your diet and HOW you do your cardio. The ABSOLUTE best way to think about your cardio routine is by using this kind of analogy...think about the difference between the physique of a marathon runner (thin, not terribly muscular looking but more wiry and very thin) and then that of an NFL wide receiver. You want to do your cardio in short bursts of intense intervals like what a wide receiver would do during each play..they sprint a good 15-50 yards each single play depending on their route and notice HOW they do their routes..VERY intense and very fast sprinting intervals. That is how you want to do your cardio routine. I like to use a stairclimber or an elliptical since sprinting kills my shins and knees now. I will go 4 minutes at a moderate pace and then every 5th minute I go so fast for that minute that I almost want to puke afterward. THEN after your "sprint interval" you want to use the next 4 minutes to "recover" meanwhile, your heart rate is still sky high anyway. You will want to make your workout about 20-25 minutes with that technique. That's it. No more than that. Do NOT do long periods of slow or moderate cardio (unless you are an MMA fighter trying to make weight) because you can see what those long periods of cardio do to your physique, just look at professional marathon runners. I would rather have a very muscular physique with as little fat as possible than be skinny and have a much smaller amount of muscle. Also, consider WHEN you do your cardio..do it first thing in the morning before you consume a single calorie and do NOT eay for up to an hour afterward, your body will still use stored fat for energy for that period of time OR you can do it late at night after you have not eaten for at least 3 hours. You don't want your body burning off calories in your system, you want to use your stored fat for energy.
That is what I do and it works great, even for an old dude like me.
Genetics do play a role, but actually, it's about lowering your bodyfat percentage; most men can start to see abdominal muscles from 10% and below while it's around 14% and lower for women. It's definitely possible for you my friend, work on cutting out saturated fat and sugar from your diet, and go on a caloric deficit (eat less calories than your caloric maintenance level) and you'll get there in a reasonable amount of time (months). Try intermittent fasting, lots of personal testimonies of losing fat and building muscle with it, and more scientific studies are being done on it. The fat will melt off slowly with IF, look it up.
Sadly, 6-pack abs are a heretary trait. If your father or brothers have them, then you can get them. If they do not "run" in the male line, you probably won't get them no matter what you do. Men who can't get those abs will find they have a thin layer of fat over the abs that "hides" the 6-pack look. The fat layer isn't like having fat cells to reduce. it is a permanent layer of fat to buffer and protect the organs of the abdomen. It is not "bad fat", it was there when you were born and will remain there. Sadly without surgery to remove the fat, you will not have the 6-pack.