A lot of heart murmurs are innocent especially in children and people who are very petite. Several reasons for that. In a smaller person, the heart is closer to the chest wall so one hears things like normal blood flow sounds that would not be heard in a bigger person. Murmurs are caused by turbulence in the blood flow. Smaller people have smaller hearts, and smaller hearts have smaller valves. Lots of blood flow through a small valve--the same principle that makes a teakettle whistle. Pediatricians are used to hearing innocent murmurs every day.
I stethed a young woman, 22 years old at the time, who was super-petite, 4' 10" 95 pounds, small rib cage, firm little 32A breasts, very visible pulsation at her PMI (I kidded her about having a beating breast--I could see that little left breast move ever-so-slightly with each beat) and over the arch of her aorta. Didn't have to guess where to place the steth for a symphony of sound! It was one of the loudest hearts I've ever listened to. Easy to feel her heart pushing against the chestpiece when I listened at her mitral. I heard a very solid s1 and s2, but I could also hear the blood flow in her aorta when I listened at her aortic and pulmonic valves. Because she was so small, what I heard was probably pretty close to what one might hear on a 10-12 year old.
I've only heard one murmur that was associated with a heart problem. I stethed a woman in her early 40s at the time who had a very harsh murmur on s2 due to a bad aortic valve with a significant amount of regurgitation. The murmur even radiated up her carotids--I could hear it when I listened to her neck. Her heart was enlarged from working so hard to compensate for the leaky valve, so her PMI was displaced to the left. She was already aware of the problem. Her father was a pediatrician, and he had detected the murmur when she was about 11. He sent her to a pediatric cardio. The valve and the amount of regurgitation had worsened over the years. She had surgery to replace the valve not long after I stethed her. I had to think about a foot long scar down the middle of such a pretty chest, but she didn't have much of a choice. Haven't had the chance to steth her since she had the valve job.
I have a friend who is 70 now who has had mitral valve prolapse for years, first detected when she was in her early 20s. No mitral regurgitation, just a clicky ticker with the "classic click" of MVP on s1. I've never listened to her heart, just heard her talk about it. I'm sure she would let me listen to her heart if I ever get down to see her and get up the nerve to ask. She is tall and slim, probably B cup breasts, so everything inside her should be easy to hear with the Littmann Cardio III.