Like many DRs here, my first exposure to SJS was the movie of West Side Story on television. In albums, it was Company - which was strangely in the collection of my parents - they had a lot of cast albums, but no other Sondheim. Anyway, I pulled it out at a fairly early age for the cover. Then I listened to it. And listened. And obsessed. And soon, I was grabbing everything the public library had on Sondheim and devouring it.
My first stage Sondheim was the original production of Sweeney Todd on Broadway. By then I was old enough to be able to travel into NYC on my own.; I must have seen the production 3 or 4 times in its original run.
That is nice that he wrote back to you, DR Jrand62. He was known for that early in his career. I wrote him a letter in the early 80's about Follies, and he was kind to reply promptly back. I don't know if that is still the case now.
I can think of no artist's entire corpus of work, other than classical composers, that has given me so much concentrated pleasure over such a long span of time. There is always something new to discover in these scores, no matter how many times you listen to them. They are witty, intelligent, sophisticated, and massively entertaining. And I am eternally grateful.