I am not familiar with the first condition, concentric hypertrophy, but you might find this helpful"
https://academic.oup.com/ajh/article/34/6/581/6265586
I am more familiar with left atrial hypertrophy/enlargement. Essentially, enlargement is in response to a stressor, usually blood pressure against the inner walls of the vessel in question...in this case the atrium. For AF, it's the left atrium. The enlargement is due to backpressure from the mitral valve that is closed due to even greater pressure on its other side by the more powerful musculature of the left ventricle.
https://www.ncbi.nlm.nih.gov/books/NBK553096/
What you should keep in mind is that the dilation of your left atrium is evident when imaged, and that it is almost certainly due to your atrial fibrillation (AF). Further, your left ventricle has mild expansion/thickening of its walls. This might be due to frequent AF, but it could also be due to hypertension systemically. If your hypertension is 'borderline', essentially low, then metoprolol can help to mitigate that. So, metoprolol has two things going for it: regulating your heart rate when you ARE fibrillation, but also generally keeping stress off your left ventricle due to mild hypertension. Note that I'm not saying you do have hypertension, only that,...IF... it is the explanation for your ventricular hypertrophy, metoprolol generally helps to reduce it.

Is any of this of major concern? I would suggest that it isn't urgent right now, but the changes do indicate a progression of your heart's general condition. If AF goes on too long, it can lead to deposition of collagen and fibrosis in the substrate of the heart (in the muscle tissue), which makes it stiffer. A stiff muscle has to work harder to make itself change length or shape in order to function properly. As anyone who builds muscle knows, when you make a muscle work harder, it adapts by making more muscle tissue. In the heart's case, it means larger myocytes, which means more volume of the tissue of the ventricle...thickening. In turn, wall thickening can lead to mitral valve prolapse, and even eventually to heart failure (not really 'failure', more like insufficiency...inadequacy).

I would ask you to take away this: the longer a heart experiences an arrythmia like AF, the more difficult it is to treat it. For example, you already have age working against you (or so you were told initially, but your lifestyle held a trump card....great!). You should really consult an electrophysiologist, ideally in person, get him/her to know you, and then you can go directly to that person when things get worse or change...bypassing the person who feels age ought to present a limit for treatment. But what I would ask you to think about, please, is that you can greatly slow the progression of your heart's disordered state by treatment, including an ablation. Ablations work wonders for many people, and if they work, they can prolong life by 10-20 years, even longer if there's no further deterioration. AF begets AF. Stem the AF and you can enjoy your life worry-free.