Salaam ...

Just tell him that following things to be seriously consider for your children planning:

1) Age factor ... more you delay more you getting close to old age and your child will be growing !

2) Children (specailly boy) runs the generation ... so to keep your generation alive you need to have kids.

3) It is a Sunnah to have Kids.

4) More ealry you have Kids ... more early they will grow you and look after you when you will be like a KID !!! you will not be able to eat yourself, your kidz will feed you, cannot go to toilet yourslef, your kids will takecare of you, you will not be able to drive, your kidz will take you around etc...

If not tell him to read my message and THINK 10times before he goes to bed.
Inshah'Allah, Allah will bless you both with a Baby soon.