Until when is it okay to nurse my baby to sleep?

Both of my kids nursed to sleep until they were about 2 years old. For my first born, she is more ready to wean herself as my milk has dried up and nothing for her to suckle. While my baby no.2, although I have no more milk during pregnant, he still continue to suck and I need to slowly wean him from nursing to sleep. It is also up to individual when do you want to wean your baby. If you wish to wait for baby to self-wean from nursing to sleep, you can do nothing but to enjoy the moment. If you intend to wean baby from nursing to sleep, you need to introduce another sleep association in order to replace your breasts, e.g. milk bottle, pacifier and etc. For me I prefer to do this gradually instead of cold turnkey as I just can't stand to let baby cries for long period.