There are two things which make a newbie unsuitable for advanced exercises.
First the issue of your penis and ligs not being conditioned and ready for things which take them close to the limits of their structural integrity.
Secondly, the issue of not yet having learnt what your penis is capable of handling and how to apply yourself to new unpractised exercises from the penis common sense you have gained from earlier experiences with the basics.
The second part takes experience and therfore time. The first part takes time and experience is a diminished factor. For instance, if somebody has gained lots of experience to know how to apply themselves in all aspects of PE, then taking several months off of PE, when they start PE again, they too will have to stay away from advanced exercises until they have reconditioned their penis again with the basics. Experience will help someone recondition their penis from scratch quicker than a newbie however and a penis may actually retain a small amount of it’s conditioning for many months on end, making it quicker to recondition for advanced work.
To put a figure on your question, I would say 3-4 months of jelqing before someone should consider doing Uli’s. 1-2 months of Uli’s before considering extreme Uli’s, Horses, cable clamps etc. This is just my opinion from past experiences.