It's recommended (not mandated) to 65+ cohort and under-65 with certain underlying risk conditions, but they won't stop you from getting it if you so wish. It

It's recommended (not mandated) to 65+ cohort and under-65 with certain underlying risk conditions, but they won't stop you from getting it if you so wish. It is also possible for people in the 18-64 year age group without underlying risk conditions can choose to take a new booster dose if they wish.