Firstly, congratulations on keeping the lifestyle strong at 48. You should be proud of yourself.
Avoidance of large muscles comes down to things like Protein intake. If you keep a fairly moderate Protein intake, and don't go crazy on your weights, then your growth potential won't be significant to yield largish gains.
You could do some strength gaining work, to help with fat loss, but when you hit a plateau, don't increase the workload, keep doing the same number of reps, even if they end up feeling light, because without that increased workload / challenge, muscle growth would be harder.
The main things would be to get the diet solid, and do Cardiovascular exercise as well.
If you get your diet right, you can get rid of fat, allowing your Abs to show through better.
Also, Metabolic function starts to decrease after 35, so that could have some impact on your Abs, being hard to notice.
That's what I think, and I'm sure others will have things to add, or politely disagree with

.
Good luck.