I think I bought my first Berkshire shares some time in the 1997-1999 area (B shares obviously). But I distinctly remember buying shares in early 2000 because IIRC it was the first time that Buffett made a statement about how the shares were obviously undervalued. Unfortunately, I was a poor PhD student at the time, so this was not a very substantial amount. But regardless of the size, it was obviously a fantastic time to invest in BRK.
More recently, I was excited to be super overweight in Berkshire when they were repurchasing a substantial of shares: