Based on prior knowledge, we can determine the appropriate ranges of values for the feature RIDAGEYR to classify individuals into the "Adult" and "Senior" age groups.

Generally, an individual can be classified as "Adult" if their age falls within the range of 18-64 years. On the other hand, individuals aged 65 years and above can be classified as "Senior".

Let's analyze the relationship between the feature RIDAGEYR and the task of predicting the age group.

- RIDAGEYR values for target class "Adult" (18-64 years):
    - Possible RIDAGEYR values: 18.0, 30.5, 40.0, 50.0, 64.0
    
- RIDAGEYR values for target class "Senior" (65 years and above):
    - Possible RIDAGEYR values: 65.0, 70.0, 75.5, 80.0, 90.0

Based on this analysis, we can create the dictionary as follows:

```json
{
    "Adult": [18.0, 30.5, 40.0, 50.0, 64.0],
    "Senior": [65.0, 70.0, 75.5, 80.0, 90.0]
}
```