At what age can children put themselves to bed?

[belgo]

My dd1 is three years old, and I still go through the bedtime routine to put her to bed, which takes about 40 minutes. My dh thinks that soon she should be able to put herself to bed, but I think she is still too young.

What sort of age should she be before she can go to bed on her own?

my 12 yo will not turn his light off before i go up, tuck him in, and a peck on his head! habit!

x posted before I saw that you said DH was being optimistic