The EFNA3 gene encodes one of the ephrins, specifically an ephrin-A class member. Here are more details regarding your requests:

### 1. Associated Genes:
EFNA3 is known to interact with several EFN receptors (EPH receptors), particularly from the EPH receptor family. Some of the key receptors include:
   - EPHB1 (Ephrin type-B receptor 1)
   - EPHB2 (Ephrin type-B receptor 2)
   - EPHB3 (Ephrin type-B receptor 3)
   - EPHB4 (Ephrin type-B receptor 4)

Other genes that may be functionally associated include those related to signaling pathways influenced by EPH receptors, such as genes involved in the MAPK/ERK pathway and the Rho GTPases which play roles in cytoskeletal organization during cell migration.

### 2. Aging and Age-Related Diseases:
EFNA3 is implicated in various developmental processes, particularly in the nervous system. Though specific studies linking EFNA3 directly to aging or age-related diseases may be sparse, ephrin signaling has been associated with neurodegenerative diseases like Alzheimer's disease due to its role in neuronal development and synaptic plasticity. Disruptions in ephrin signaling may contribute to pathologies associated with aging, including:
   - Neuroinflammation
   - Cognitive decline
   - Vascular changes

### 3. Drug Interactions:
Currently, specific drugs that target EFNA3 or its pathway may not be well characterized. However, it is important to note that pharmacological interventions targeting Eph/ephrin signaling are being explored in various contexts, including:
   - Cancer therapies: Disruption of Eph/ephrin signaling has been implicated in tumor progression and metastasis.
   - Neurodegenerative disease therapeutics: Compounds that modulate Eph signaling pathways might have therapeutic potential.

### 4. Pathways and Biological Processes:
EFNA3 is involved in several key biological processes:
   - **Cell Adhesion**: EFNA3's interaction with EphB receptors facilitates cell-cell contact and adherence, crucial during development.
   - **Neuronal Development**: It plays an essential role in the guidance of neuronal growth cones, thereby contributing to the establishment of neuronal networks.
   - **MAPK and Rho GTPase Signaling Pathways**: EFNA3 participates in downstream signaling cascades once it binds to its Eph receptors, activating pathways that regulate cell migration, proliferation, and differentiation.
   - **Angiogenesis**: It may also have a role in blood vessel formation due to its association with vascular development.

In summary, EFNA3 serves as a crucial player in multiple biological processes tied to neuronal and vascular development, with potential implications in age-related pathologies and therapeutic avenues targeting its signaling pathways.