Other specific traditions (both Traditional and Modern) will have differering requirements which may include study (either general or specific to that individual tradition), demonstration of ability or knowledge, dedication (to deity or to the secrecy of the individual tradition) or simply a long enough period of committed interest to justify taking the interested party forward.
While all of these restrictions can be valuable within a community, to my mind they all pertain more to the interests of the group the individual wishes to join than they do to the actual crossing over from a non witch to a witch.
I do personally believe that a certain formality is necessary in the making of a witch. I don't subscribe to the esoteric idea of indoctrination into secret traditions (and certainly not the degree system which seems to achieve very little other than making the self important feel even more self important) but I do believe that to effectively follow a craft path there has to be a definite demarcation, a parting from the old life and an embracing of the new. However I dislike the idea of the structure of this being imposed on an individual and if I were a novice witch I'd run like hell from anybody who wanted to design my crossing over ritual for me.
A witch knows when its time to make that break and take that step forwards and its important that the decision is hers and also that the method of taking that path is hers. Frankly if somebody told me they felt ready to practise the craft but didn't feel up to understanding their own ideas of formalising their path I'd tell them to give it a lot more thought because they simply wouldn't be ready to take the step. I don't care how long a person has been practising, if they aren't yet at the stage where they can write their own spells and rituals they need to consolidate their abilities before trying to progress further. Equally the length of time a person has their head stuck in a book wouldn't be a factor for me. If you know what you want and you know how to achieve it, it's silly to wait just because other people have an expectancy that you read your way through the witchy library first.
Don't get me wrong, the details of the crossing over may vary between individuals wildly. For some it may just be a very simple realisation that the path has been chosen, for others it might be a hugely ceremonial ritual. I'd regard the two as having no difference in merit but I do think it important that there is a specific point where you confirm to yourself that you are both ready to pursue the craft with the commitment it deserves and that you are willing to do so.
Speaking personally, I'm very fond of ceremonial magic and my crossing over was rather a dramatic work of art... Interestingly enough I had been practising magic for some time before but when I made that formal commitment to myself and my craft my own abilities sky rocketed. The focus, the determination, the dedication and the pledge to yourself and your craft can be key to helping you realise your own individual potential to being the best witch you can be.