Dr brown pacifier? Safe until when?

M ❤️ • 30 years old. TTC 2 years, froze eggs 11/15, FET 2/16, 1/16, 3/16... Due 11/16 had baby boy 11/16 ... some how naturally pregnant and due 11/17

Our LO is 10m and still using the 0-6m old dr brown silicone pacifier. We give him different pacifiers and he won't accept them. The recommend age is to 6m but I can't find anything saying why. Is it safe to still give him these ?