This group of slings are very similar to the Chinese / Asian style Mei Tai's - a square of material with 4 straps. These clip together with buckles rather than tying, some have thick waist bands for lumbar support.
Note - Age guides are based on my personal experience of hiring these slings out and using
myself. They have got wider safety limits however become less supportive and comfortable when used upto the limits. Do contact me to discuss your requirements if you are