Based on prior knowledge, we can analyze the relationship between the feature RIDAGEYR (Respondent's Age) and the target variable age group (Senior or non-senior) as follows:

1. Senior: It is reasonable to assume that individuals in the age group of 65 years and above are considered seniors. Therefore, values of RIDAGEYR greater than or equal to 65 can be classified as seniors.

2. Adult: In this case, we can consider the non-senior age group as adults. However, since there can be a wide range of ages within the adult age group, it is challenging to determine an exact range from the given information. Without any specific guidance, we can assume that adult age ranges from 18 to 64 years. This assumption can vary depending on the context or definition of the term "adult."

Based on this analysis, the dictionary for the feature RIDAGEYR can be constructed as follows:

```json
{
    "Adult": [18.0, 25.0, 35.0, 45.0, 55.0],
    "Senior": [65.0, 70.0, 75.0, 80.0, 85.0]
}
```

Please note that the above age values are just examples and can vary depending on the dataset or specific context.