Serious answer: No. If you have ADHD, you have always had ADHD.

But some ADHD symptoms can be experienced without having ADHD. ADHD is identified by a bunch of symptoms and, importantly, the degree to which they affect one's life.

But anxiety and depression are common causes of some ADHD-like symptoms. My bestie suffers from anxiety and absolutely has some ADHD-like symptoms. But doesn't have others.

And neurotypical folks often have some ADHD-like symptoms, but it's to the degree that it impacts them and/or it could come from a different cause. Or some folks find out later in life they have ADHD. (I was 30 - same for my wife, who found out at 50 she was actually AuDHD)