New driver-independent-age requirement?

OK guys, I’m looking to get a little insight on this plan I’ve had. I’m 20 years old and getting my CDL next month. I’ll be buying my own used day cab and a 53 foot dry van trailer. 21 seems to be the minimum for every company out there so what I’ll be doing is picking up loads off of online load boards. Do the companies hiring you for these loads also require you to be a certain age? I’ve looked on the one online load board and see plenty of intrastate hauls with decent pay. Thanks in advance

 

Insurance will definitely be a pain, I’m dreading getting a quote. I don’t mind only doing intrastate hauling for the next year, my question is more of will I be allowed to take loads from load boards at 20.