Took first puff on a Newport around age 10, but didn't really "smoke"' one until I was 14... bought my first pack just after I turned 16, became a "real" smoker around 17-18 but never had that much trouble cutting back or doing without... I dunno, guess I was spared a propensity to really get "addicted" to cigarettes (or other tobacco -- while down South, I did try out dipping). After the last 5 years primarily vaping, I find a cigarette so much more intense, and I really don't think I have any dependence on "nicotine" in the vape at all. (Without all the MAOIs in tobacco enhancing it, nicotine hasn't been proven to be "an addictive chemical" as the warning labels claim.)
Earliest memory of alcohol intoxication is around age 8-9 at the Italian family reunion of one of my dad's friends. For some reason, maybe boredom, I went around drinking the beer out of several plastic cups left sitting on tables, until I found myself feeling great while urinating with extreme intensity. Eventually, I sat down with some "teenagers" (who I normally would've been mortally afraid of) and started talked to them about COPS (the TV show)...even picked up the acoustic guitar they were strumming and banged away at it while they laughed ("this kid's drunk!"). Good times.
I started drinking regularly around age 13, but didn't really start binging until 16-17 and became a nightly drinker around 18-19 (which I remained for almost a decade with scarcely a night off, until I traded up to opiate addiction). First tried marijuana around age 14, didn't get much out of it; started to smoke periodically around 16, still didn't get much out of it; started to smoke seriously around 17-18, still didn't get much out of it; kept sampling it as I became an alcoholic and addict, now I got something out of it -- crippling guilt and fear! Actually, marijuana was my "anti-drug" (as the PSAs went): while high and hating myself, I almost always ended up making solemn resolutions to kick the alcohol/benzos/dope/etc. and start living right.
Earliest memory of opiate intoxication is around age 7-8 after I broke my leg in a bike crash. My mother fed me something bitter (Tylenol #3?) crushed up into vanilla ice cream. Half an hour later, I was nodding off on the couch, eyes closed, watching my own TV shows in my head, feeling good -- feeling better than good, actually.... a feeling I never forgot even though I was separated for a while (until 15-16, when I started dipping into my dad's hoarded Vicodin).