The MIR558 gene encodes a microRNA (miRNA) and plays a significant role in gene regulation by targeting messenger RNAs (mRNAs) for degradation or translational repression. Below is a detailed summary based on your request:

### 1. Associated Genes
While specific genes directly associated with MIR558 may vary depending on the target interactions predicted or demonstrated in the literature, potential target genes can include those involved in various pathways such as cell cycle regulation, apoptosis, and stress responses. Specific examples of predicted targets of MIR558 may include:
- **BCL2** (B-cell lymphoma 2): Involved in the regulation of cell death.
- **MYCN**: A transcription factor that can be associated with oncogenesis.
- **MAPK pathways**: Components of signaling pathways that modulate various cellular processes.

These associations are typically found by analyzing miRNA target databases like TargetScan, miRanda, or through experimental validation studies, which may not be detailed in NCBI or UniProt summaries.

### 2. Aging and Age-related Diseases
Research into the role of miRNAs, including MIR558, in aging is still developing. However, certain miRNAs have been implicated in modulation of cellular senescence, inflammation, and responses to stress, all of which are critical in aging processes. Specific known or proposed associations of miR558 with age-related conditions may include:
- **Neurodegenerative diseases**: Changes in miRNA expression profiles, including MIR558, have been linked with diseases such as Alzheimer’s.
- **Cancer**: Some studies suggest that alterations in the expression levels of miR558 may influence tumorigenesis, which tends to have a higher incidence in aging populations.

### 3. Drug Interactions
While specific drug interactions with the MIR558 gene itself may not be thoroughly characterized, miRNAs can influence drug efficacy and resistance through the regulation of their target genes. There are some drug classes that can be affected by miRNAs:
- **Antineoplastic agents**: Certain miRNAs, including MIR558, may regulate genes involved in cancer cell response to chemotherapy.
- **Anti-inflammatory drugs**: Given that miRNAs modulate inflammatory responses, there might be relevance in therapeutic contexts targeting inflammation.

However, specific small molecule drugs or drug classes directly interacting with MIR558 have not been clearly identified in available literature.

### 4. Pathways and Biological Processes
MIR558 is involved in several biological processes and pathways, largely mediated by its role in regulating gene expression. Notable pathways include:
- **Regulation of gene expression**: Plays a direct role in the post-transcriptional regulation of various target genes.
- **Apoptotic signaling**: It influences pathways that govern programmed cell death, impacting both normal physiology and cancer biology.
- **Cell cycle regulation**: miRNAs can control the expression of genes involved in the cell cycle progression.
- **Developmental processes**: miRNAs are critically involved in various developmental pathways and tissue differentiation.
- **Response to stress**: Involved in pathways that mediate cellular responses to oxidative stress and other adverse conditions.

The precise roles and mechanisms of MIR558 in these processes may involve complex interactions with multiple genes and proteins which warrants further studies for complete elucidation. 

### Summary
MIR558 is a significant regulator of gene expression via its miRNA product, influencing multiple biological processes and possibly participating in the regulation of aging and age-related diseases. While specific drug interactions may be less defined, it forms a pivotal part of pathways crucial for cellular responses, making it an important target for further research in therapeutics and pathology.