You are not required to tell your best friends every single secret, however, if you truly want to tell them you should. Friends are supposed to be supportive, and having a crush at nearly any age is totally normal. Not having a crush or never feeling attracted to anyone is also totally normal, as some people may take longer to feel this way, and some just do not have an attraction to anyone (Asexual, Aromantic). Your friends may feel uncomfortable because they are not comfortable with having a relationship at that moment in their lives. If you are sure that you yourself are comfortable with having a crush and possibly acting on it, GO FOR IT!!! You do not need your friends' approval for everything, as peoples' opinions may differ. When telling your friends, make sure to be firm and assertive. If you truly feel a certain way towards any topic, do not change your opinion because of what the majority believes.
I hope this helps!
-GymnastPower, Girl's Advice Column President