I practice and instruct judo, where my advice to beginners is to seek the most experienced and skilled practice partners available. My experience is the normal beginner tendency is to train with partners of the same skill level. Unless players are adhering to a rigorous competition training program or there is a safety issue, the expectation is you practice with people who ask.
I was recently informed by a BJJ practitioner cross-training in judo that she was explicitly discouraged in BJJ from asking experienced (brown? and black belts) to practice together during a training session. The expectation was the more experienced practitioners would choose their partners. Is this normal procedure in BJJ or a local quirk?