The 6 month oil change schedule covers a wide range of driving conditions. An owner that drives 3 miles each day should have the oil changed every 6 months, an owner that drives 30 miles every 10 days, perhaps not really necessary but the maintenance schedule isn’t written for multiple conditions, that would be too confusing.
I have a number of senior customers that don’t drive everyday and change their oil every 18 months, these include the RX300/RX330/RX350. If engine sludge were a problem we would recommend that they change their engine oil more frequently.
I also have some customers that follow the book, changing the oil every 6 months. Last month a GS430 came in for an oil change, emissions test and to have the battery recharged, the car had 14 miles since the last visit, I suspect that they live 7 miles away. There are people on this message board that are no different.
Change the engine oil at your own discretion based on use. I have 4 vehicles that call for oil changes every 3000 miles/ 4 months, I change the oil once a year/5000 miles on two of them and every other year on the other two.