Interdigital candidiasis (athlete's foot): This is a common fungal infection that causes inflammation, redness, and swelling between the toes, especially in warm, moist environments. The absence of systemic symptoms and the location of the swelling make this a likely diagnosis.

Eczema (dyshidrotic eczema): Characterized by small, itchy blisters on the hands or feet, eczema could cause swelling and redness between the toes.
Contact dermatitis: An allergic reaction or irritation from substances like soap, detergent, or certain materials in shoes could lead to similar symptoms.
Ingrown toenail: If the swelling is localized near a toenail, an ingrown toenail could be the cause, especially if there's redness and tenderness.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth. Although the patient doesn't have a fever or body aches, cellulitis can sometimes present without systemic symptoms, especially in its early stages.
Deep vein thrombosis (DVT): While less common in the foot, DVT can cause swelling and redness. Given the potential severity of DVT, it's crucial to consider, especially in older adults.
Erythrasma: A bacterial infection that thrives in warm, moist areas of the body and can cause redness and swelling between the toes.

Pitted keratolysis: A bacterial infection that causes small pits in the skin of the feet, often accompanied by a foul odor. It could potentially cause some swelling and redness.
Keratoderma: A group of rare skin conditions that cause thickening of the skin on the palms and soles, potentially leading to swelling and redness between the toes.

Given the symptoms and duration, the most appropriate next steps would include:

Keeping the area clean and dry
Applying an antifungal cream for athlete's foot
Considering over-the-counter hydrocortisone cream for eczema or contact dermatitis
If symptoms worsen or do not improve, consulting a healthcare provider for further evaluation and possible prescription medication.