5 years to understand basic documentation and diligence (ie most usual investments and partial exits) and around 10 years to understand the more complex adjustments in M&A documents (ie more the "why" of those adjustments rather than the drafting of those adjustments - an understanding where you will be able to help the client add exceptions to adjusted working capital, adjusted net debt, or adjusted EBITDA definitions which the client may not have considered) and tax structuring.

I have never met an associate with 4 years of work experience who actually understands most of the adjustments or even the least bit of tax structuring. I think a lot of associates with 3/4 PQE think they understand the work a lot more than what they actually do - knowing terms doesn't mean you actually understand the concept. I find most partners in law firms don't know even basis tax provisions relating to PE / M&A deals and hence suggest structures which are non-starters. Even provisions which come up frequently during discussions, such as 195/197 or 281, most partners don't know what position to take on these and why these positions must be taken - very few have done the background research.

In the larger law firms, most kids are doing diligence for the first 3/4 years and they understand documentation and negotiations even lesser than associates of smaller law firms who have been a part of that side of a deal. I don't see how most of these kids will know which items should be an exception to normalised working capital or net debt, other than copying language from another draft.

You may very well be an exception and, if so, you will probably become a partner in 5/6 years; if you completely understand your work at this stage of your career.