The concern is understandable and it's a question that comes up a lot.
The honest answer is that taking it three times a week will still suppress DHT meaningfully. Finasteride has a half life of around six hours, but the DHT suppression effect lasts significantly longer, up to several days after a single dose. So alternate or reduced dosing does still work to a degree.
Whether it meaningfully reduces side effect risk is less clear. The available data suggests DHT suppression is still substantial even on reduced dosing schedules. Some people do report better tolerance on every other day or three times a week dosing, but this is largely anecdotal rather than well studied.
At 53 the hormonal context is also different from a younger patient. DHT plays a role in various physiological processes, and the impact of suppression can vary with age.
If side effects are the primary concern, topical finasteride is worth discussing with whoever prescribed it. Systemic absorption is significantly lower than oral and many patients who are worried about sides find it a more manageable starting point.
Starting low and slow is not unreasonable. Just go in with realistic expectations about what reduced dosing will and won't change.