The EN2 gene, or Engrailed 2, is a highly conserved gene within the homeobox family, playing a critical role in the development of various organisms. Here’s a comprehensive overview fulfilling your specific requests:

### 1. Associated Genes:
While the provided summaries mention the mouse homologs En1 and En2, there are other genes associated with EN2, including:
- **EN1 (Engrailed 1)**: Shares a high degree of sequence similarity and is involved in similar developmental processes.
- **WNT signaling pathway components**: Various components (like **WNT5A**) can interact with the expression and function of EN2 during neural development.
- **SHH (Sonic Hedgehog)**: This signaling pathway is known to interact with EN2 during early embryonic development, especially in patterning the central nervous system.
- **Gbx2 (Gastrulation Brain Homeobox 2)**: Another homeobox gene implicated in regionalization of the developing brain and associated with EN2 function.

### 2. Aging and Age-related Diseases:
There are emerging studies suggesting that EN2 may play a role in neurodegenerative diseases. Some key points include:
- **Role in Neurodevelopment**: Variations or dysregulation of EN2 expression may contribute to neurodevelopmental disorders, which can have aging-related implications.
- **Alzheimer's Disease**: Studies suggest that homeotic genes, including EN2, may have roles in neurogenesis and maintenance of neural circuits, which are disrupted in diseases like Alzheimer's.
- **Potential Association with Parkinson's Disease**: While more preliminary, some studies suggest a potential link between EN2 expression levels and neuronal fate in the context of aging and neurodegeneration.

### 3. Drug Interactions:
Research surrounding direct pharmacological interactions specifically influencing EN2 is limited. However, pathways associated with EN2 (such as the WNT signaling pathway) may theoretically interact with:
- **GSK-3 inhibitors**: Drugs targeting glycogen synthase kinase 3 (GSK-3) could influence the WNT signaling pathway and thereby potentially modulate EN2 activity.
- **Histone deacetylase inhibitors (HDACi)**: These may alter gene expression patterns, possibly impacting homeobox gene regulation, including EN2.

### 4. Pathways and Biological Processes:
EN2 is involved in several critical biological processes, including:
- **Developmental Patterning**: EN2 is fundamentally involved in controlling segment polarity during embryonic development, particularly in the central nervous system.
- **Regulation of Gene Expression**: As a transcription factor, EN2 directly influences the expression of numerous downstream target genes essential for proper neurodevelopment.
- **Neural Development**: Specifically, EN2 is instrumental in the development of the midbrain and hindbrain regions, including aspects of axon guidance and neuronal subtype specification.
- **Cell Proliferation and Differentiation**: EN2 has roles in regulating the proliferation and differentiation of neural progenitor cells.

### Conclusion:
The EN2 gene represents a critical component of developmental biology, particularly concerning the nervous system. Its functions extend into various pathways, and while there is some suggestion of links to age-related conditions, further research is needed to elucidate the exact mechanisms and therapeutic implications. The association with homeobox genes and signaling pathways adds depth to its importance in both early development and potential disease contexts.