Even at 42 I'm glad you discovered something you didn't know you were missing. Fun, ain't it.
Most have suggested some sort of .22. Could not agree more. Now your choice will be longarm or handgun.
If I were just starting out from scratch....no guns (sorry, freaking myself out imagining that I had no guns at all....
)....I'd personally go with a .22 rifle first.
Then a .22 handgun. Revolver or semiauto.
A single shot 20gage would be third.
.357 mag revovler, forth.
Semiauto 9mm, fifth.
That is just my personal tier, but that is exactly where I'd start.