I don't think that heart problems are associated with age per se but, instead, are associated with the length of time a person's lungs have had serious damage - especially if the person hasn't been using oxygen during that time and their O2 levels have been under 90 for years.
An underlying heart problem is also possible as well. My husand had both bronchiectasis and Marfan syndrome (which effects heart valves). He was set up for heart failure. That's one reason they put him on calcium channel blockers and O2 really really early.
You can't know what's really going on without the tests tho. So docs may ask abouot retaining fluid (puffy ankles and such) and let you know for what reason they are asking, but they can't really make the diagnosis without the tests (doesn't sound like your doc has actually). Maybe your doc is just treating you like the grownup you are and letting you know what the possible concerns are and why he/she would like to do tests (and I would insist on the tests - at least on an echocardigram).