SNORD121B, also known as a small nucleolar RNA (snoRNA), is involved in the biogenesis of ribosomal RNAs and modifications of other non-coding RNAs. Specific information on this gene is somewhat limited, so let’s evaluate it based on what’s available and infer relevant associations.

### 1. Associated Genes:
The SNORD121B gene may be associated with several other genes involved in similar biological processes, particularly those linked to RNA processing and modification. Commonly associated snoRNAs include:
- **SNORD121**: Related snoRNA that is functionally similar to SNORD121B.
- **U3 snoRNA**: Plays a role in the processing of pre-ribosomal RNA and is functionally related to several snoRNA genes.
- **Other snoRNAs**: Such as SNORD14 and SNORD29 that partake in snoRNA-related processes.

These associations are often inferred through studies of snoRNA families, as they typically function in similar pathways.

### 2. Aging and Age-Related Diseases:
Currently, there are no direct studies linking SNORD121B to aging or specific age-related diseases. However, perturbations in snoRNAs, in general, have been implicated in the regulation of cell growth, proliferation, and apoptosis. As these processes are critical in aging and age-related diseases like cancer, further research may uncover more details:

- **Cancer**: Changes in snoRNA expression have been frequently observed in various cancers, which may indirectly connect SNORD121B with age-related tumorigenesis.
- **Neurodegenerative Diseases**: Some snoRNAs have been associated with neurodegeneration, although specific links for SNORD121B have not been firmly established.

### 3. Drug Interactions:
Currently, there are no specific drugs or drug classes known to interact directly with SNORD121B. However, since it participates in ribosomal RNA modification and gene expression processes, factors that affect ribosomal function or RNA behavior may have indirect implications. Common drug classes that may intersect with the general snoRNA function and ribosomal activity include:
- **Antibiotics** that target bacterial ribosomes (e.g., aminoglycosides) may indirectly provide insights into RNA interactions.
- **Oncology drugs** that affect RNA synthesis could potentially affect snoRNA activity but require more specific studies.

### 4. Pathways and Biological Processes Involvement:
SNORD121B is implicated in several biological processes and cellular pathways:
- **Ribosome Biogenesis**: This gene plays an integral role in the processing of pre-rRNA and post-transcriptional modifications necessary for ribosome assembly.
- **RNA Modification**: Through the formation of ribonucleoprotein complexes, SNORD121B is involved in 2'-O-methylation of ribosomal RNA, influencing its stability and function.
- **Cell Division and Proliferation**: The regulation of RNA modification is crucial for proper cell cycle regulation.

As with many snoRNAs, ongoing research may yield more insights into the specific roles and implications of SNORD121B in both normal physiology and pathophysiological conditions. More investigations are necessary to uncover connections related to aging and age-associated diseases or drug interactions.