I think 2 years is a good minimum to start applying to CRA I jobs at the major CROs; however, right now the big companies have a lot of needs, so I would not wait. Apply today at those big (and small) CROs- you can always try again next year.
CRCs my company is hiring for CRA 1 roles on average have 5 years.... But many have upwards of ten years for personal reasons (wanted kids to grow up before they started traveling so much).
As a baseline, you should also have a Bachelor's of Science degree. It doesn't matter if it's nursing, biology or healthcare.... It should just be a BS. Also, you must work in every phase of a study (start up, initiation visits, monitoring visits and close out visits) and know GCPs about the monitor's responsibility at each visit.
You will not get a CRA 2 position- by definition, you need CRA experience to be a CRA 2. But, if you see a job offer on a website for a CRA 2 job- apply anyway. If you get hired, they will give you the right title. When I was looking to change jobs two years ago, I was at the senior level but could only find job posts for CRA2 - I applied anyway and ensured that when I was hired, my job title would reflect my experience level. The 1, 2, 3, senior and princlal levels are just a measurement of experience and job duties do not differ by levels.