Walk into Sultanahmet Square to admire Hagia Sophia from outside and enter if lines and opening hours permit (Hagia Sophia typically open 9:00–19:00, last entry earlier). It's an iconic start and easy on the feet.
Visit the atmospheric underground cistern with its Medusa columns and cooler temperatures — it usually stays open until around 18:30–19:00, so this is a good evening slot.
Admire the Blue Mosque’s façade and enter briefly if it isn’t closed for prayer (the mosque is closed to tourists during prayer times); the square is peaceful in the evening.
Take a 1.5–2 hour Bosphorus cruise to see palaces, wooden mansions and bridges from the water — public and private options run throughout the day (typical departures 9:00–17:00).
Climb or take the lift up Galata Tower for panoramic views of Istanbul — the tower is generally open 9:00–19:00 and offers excellent photo opportunities.
Wander Istiklal Avenue’s shops and arcades at a leisurely pace, take a nostalgic tram ride and rest at a café; it’s lively but manageable for older travellers.
Have a simple breakfast before boarding the ferry — you’ll want energy for the island strolls while keeping the pace easy for the older members of the family.
Choose a horse-drawn carriage for comfort or rent bicycles (electric if preferred) to explore the island’s wooden villas and scenic viewpoints at a relaxed pace.
Explore the Grand Bazaar’s covered lanes for carpets, ceramics and souvenirs — it’s lively but most shops open from about 9:00 and it’s wheelchair- and older-person-friendly in many areas.
Take a short trip to Pierre Loti hill for tea or coffee with a beautiful view over the Golden Horn — accessible by cable car and a peaceful way to relax before leaving.