Based on prior knowledge, let's assume that a BMI value below 25 is considered normal weight and a BMI value of 25 or above is considered overweight. We will use this to determine the appropriate ranges of values for the target classes.

Based on this assumption, we can create the following dictionary:

```json
{
    "Adult": [18.5, 19.7, 21.3, 23.1, 24.8],
    "Senior": [26.5, 27.9, 29.6, 31.4, 33.2]
}
```

Explanation:
- For the "Adult" target class, we selected 5 typical BMI values that are below 25 (normal weight).
- For the "Senior" target class, we selected 5 typical BMI values that are 25 or above (overweight).

Please note that these values are just examples and may not reflect the actual distribution of BMXBMI values for the target classes. To create a more accurate dictionary, a thorough analysis of the dataset is required.