When my plants were 5-6 weeks old, they were about about 14"+. And I had mess'd up the first 3 weeks.
How did you Germ, and plant your seeds? What are they planted in? Looks to me, like that soil is mostly ground up wood. Which most soils are that way now. Did you add any perlite for drainage? Looks to me like you didn't.
Replant them in soil that is well mixed with Perlite, and try to get soil with no time released Nuts. Remember, When you think you have enough perlite for drainage, add a good bunch more.
TIME RELEASED SOIL GARGLES NUTS..
Time released is just that. If you get time released Nuts in your soil, you can flush the living hell out of it, it will still have those TIME released nuts. There is soil out there that is truley soil, (not ground up wood). Which is Sterile, and has zero time released nuts. Most of the commercial brand soils, have time released nuts.
My woman wishes I had time released nuts, But I do not like them.