Ive just googled to see what age people start doing it.
I found the baby whisperer forum, which is entirely dedicated to pick up put down method. Just thought it might be helpful x
https://www.babywhispererforums.com/index.php?board=31.0
This is what was said about what age to use the method
This is a tricky question. You should definitely not use it below three months of age as babies below three months old are too stimulated with the picking up and putting down and they burn far too many calories in the process. Between 3-4 months is a bit of a gray area. For many babies, pu/pd may still be too stimulating and, therefore, unsuccessful.
For babies younger than four months, the primary babywhisperer tool for sleep training should be the “Four S” wind down and the shush-pat method. To wean a pacifier in a young infant, consider trying the Gradual Weaning Process; to wean feeding-to-sleep in a young infant, consider trying the Gentle Removal Plan.
Generally, you can use a version of pu/pd with a baby of four months or over; however, even some four month olds are not ready for it so you should always try shush-pat in the first instance. It’s best to wait as long as you can; generally by 5-6 months most babies are ready for PU/PD. Again, it’s best used if all other methods have been tried and have failed.
