Once you have decided after careful reflection, treat him with the greatest respect and beg of him to accept you as a disciple. You are fortunate if he does, because a true master is not fond of collecting hundreds of disciples. Rarely does he agree to be the guru.
A guide is necessary in almost all cases because you are starting on a voyage of largely uncharted territory. You may find here and there greatly advanced spiritual beings who do not seem to have had a guide. They are exceptions, and though they may not have a guide in human form, understand that God Himself guides them and looks after their needs.
Don’t imitate them, for they belong to a special category. Do not even imitate your own teacher for you are not he. Follow his teachings and instructions instead and you’ll bloom into a master in your own original way and not turn out to be a faint imitation; a shadow of the original.
A master may be young, old, male, female, fair or dark. The externals do not matter at all. What matters is his inner spiritual status. He may, if he so decies, help you wipe your heart clear of all the accumulated vasanas and make you free.
May such a master guide you!