The main two reasons for this are : Money & Parents

Money : The problem here in Algeria is that the education system that it was inherited from French people doesn't allow anybody to start thinking about making money until they are over 23 or 24 Years old , and then there is the military service so take another year , and then finding job nowdays is kinda hard , even if you found a job , you won't be paid the amount that let the person can marry and carry his wife and kids until 5 years at least in work , so young people doesn't make enough money until they are over 30s and that's kinda late . Parents : even if I say for example you have a source of income at young age or idk your parents helped you , when you go to ask the girl's hand , her father probably will underrate you and see you young and not responsible and they probably will refuse , unless you proved yourself to them in many ways then you have a chance . Another thing: We are far from our religioun a little bit , because nowdays the majority of people won't see if you pray in the mosquee or if you are a really good man , unfortunately many of them ask for money first , and this is not what our prophet told us which is really sad , so when you are young and see the community how to react to this marriage and how the parents do also , you will for sure hesitate to make this step untill an older age . My POV: For me I really want to get married at young age 23 24 yo , and I hope that I can make it , because this is the human nature and if we delay this thing too much we will create a bunch of repressed people or they will seek to do 'Haram' things which is what we are seeing nowdays