To determine the appropriate ranges of values for the feature LBXGLU in relation to the target variable (age group), we can assume that higher blood glucose levels may be more common in older individuals. 

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

```json
{
    "Adult": [70.5, 85.2, 92.1, 96.8, 100.4],
    "Senior": [95.6, 110.3, 118.7, 122.9, 135.2]
}
```

Please note that the provided values are just examples and are not based on real data. You should replace them with actual values from your dataset or consult relevant medical guidelines for more accurate information.