The typical prerequisite to becoming a Private Equity Associate is working at an Investment Bank or major consulting firm for 2-3 years. Most established Private Equity firms typically make hiring decisions nearly two years in advance of their start date, so many people will interview for their Private Equity job shortly after starting at their IB or consulting job. However, there are many small, less established Private Equity funds that will hire with different requirements and on different timelines. These funds are more of an unknown, but you will likely be an earlier employee (and therefore have a higher long-term upside). And of course, even established firms will have hires drop out or quit unexpectedly and will occasionally hire on shorter timelines.
Note also that it is very, very difficult to get a Private Equity job at a middle-market or larger fund if you have an MBA, but you do not have pre-MBA Private Equity experience.
Life as a Private Equity Associate can be intense. Typically you should expect to work 60-80 hour weeks and juggle multiple responsibilities at once. An associate is typically responsible for building financial models in Excel, performing on-the-ground diligence, and preparing investment materials. At most firms, you'll juggle multiple projects with multiple bosses all at once, and will constantly be in a push-pull between what allows you to do the best job and what you have time to do. The associate position is the entry level position, so you should expect to do much of the grunt work for your team. It is a good stand-in for a "case method" business school experience, in that you will review and discuss a huge number of businesses and join in on discussions with people much more experienced than you. It involves regular but somewhat infrequent travel (once or twice per month) as you visit prospective companies and/or companies your fund already owns.
There are two reasons someone might want to be a Private Equity Associate. The first reason is if you want to make a lot of money. Even at the entry level, these jobs pay more than almost any other job you can have at a similar level of experience, and ultimately being promoted into a senior position at a successful firm can make you obscenely wealthy. The second reason is if you want to experience a boot camp for running your own business. A 2- or 3-year Associate program at most Private Equity firms will teach you a tremendous amount about accounting, corporate fundraising, budgeting/planning, and other nuts-and-bolts of corporate finance. At firms that assign Associates to work at portfolio companies, you'll also get to sit in at board meetings and have an up-close view of the challenges of running a large business. There are few jobs available (at a similar experience level), which can give you as many "reps" of hands-on experiences.
Typically lots of free meals and travel perks
A long-term career in this industry is a big gamble. Your success is based both on your own ability to get promoted and the general performance of the firm - i.e., if the firm makes some bad investments, there will be limited opportunity to move up in the firm, even if you are doing a great job. And until you are a partner / senior member of the firm, work-life balance can be very difficult, and the work you are doing can feel unfulfilling. What's more, it's very difficult to make a lateral move to another firm once you are more senior than the entry-level position. Typically, those who leave their firms are limited to going to brand new firms or starting their own. Even just the 2- or 3-year Associates program can be very intense and taxing on your personal life. Most Private Equity jobs are better work-life balance than Investment Banking, but not by too much.
Short of starting your own business, there is arguably no job you can take that has a higher earning potential than this one. The most senior non-founder leaders at the largest firms are billionaires or near-billionaires. Even at a middle market firm, a non-founder senior partner can make north of $20M per year. And even at the middle levels the pay can be very attractive. A New York-based middle market fund will typically offer its lowest level middle managers north of $1M annually in their first 5 years, although much of this will be incentive based on individual and firm performance.
The vast majority of PE funds use headhunters to search for their Associates. The headhunter used will depend on your background - headhunters will specialize in investment banking recruits, or consulting recruits, or former operators, or etc. Understanding what types of funds are looking for your background and then finding their headhunters is the first and arguably most important step.
It will depend on the firm, but most Private Equity companies are overwhelmingly male. Many firms have a reputation for being somewhat fratty, but especially over the past 5-10 years a lot of these firms have shifted into being a lot more unapologetically nerdy. As for diversity, there is significant diversity in some senses and a total lack of diversity in other senses. At my firm every member of the investment team (at all levels of seniority) was an immigrant or the child of immigrants. The majority of the Associates were non-white, and there was a large amount (and growing) of South Asian and East Asian representation at all levels of leadership. On the other hand, I did not meet a single black Associate at any of the firms we mingled with in the area. Women probably made up 30-40% of the Associate classes I interacted with in the area but a tiny sliver of industry leadership.
The vast majority of established funds are in New York or Boston. There are some very reputable funds in California, Chicago, and Texas, but a lot fewer. But there are tons of unestablished funds in all cities, which can offer some appealing opportunities.
Getting promoted in this industry involves factors in and out of your control. In order to get promoted at any fund, you'll need to be able to put in long hours, get along well with senior members of the firm, learn new things quickly, and show great attention to detail. But you also will need to be working at a fund which is making successful investments and continues to grow, because firms can only promote aggressively if they are expanding aggressively.
To be totally honest, there is a very ominous tail risk on a long-term career here, which is that public policy changes could rock the industry. There are 2-3 simple laws which would severely impair the long-term earning potential for the top earners in the industry - and, to be honest, some of these changes may be warranted, reasonable, and politically popular. If you are just looking to break into the industry now, it may be 15-20 years before you reach the senior level of a successful firm. There will be at least 3 different Presidents during that time. If you're pursuing a long-term career in Private Equity, you should be doing it with a lot of tolerance for risk.