You can tell him:
1) high % of getting healthy kids if preggy when you younger
2) do you want to be an old parent when your kids are still so young?
3) baby not say want will confirm have one... you wont know if theres any issue until you really start trying for one. Tink conceive is so easy? Takes time also...some ppl drag & drag...when they really want to have one...too late....infertily issues...
4) No one is totally ready for a baby arrival.... you do & learn at the same time...theres no school for parenting... everyone learn along the way..
5) you can retire earlier
For my case, we always wanted to have a baby asap after marriage. Marry at 26, preggy with lst baby at 27, preggy with 2nd baby at 28.. The many hardshipss of their babyhood days is mostly forgotten...now i can enjoy their toddlerhood.. Its tougher on you to be preggy when you are older ..physically & emotionally.... dont get me started on... complications during pregnancy..etc etc. so best is asap.