I have a thirty year old t-shirt that was a large and it now wouldn't even fit a five year old. What gives?

Holy crap! A 30-year old t-shirt!

geeez....maybe it was made with extra-shrinking fabric...

If you are considering wearing it, maybe (if not too disrespectful) you could cut it into pieces and sew it on to a new, less shrinkable shirt.

I learn in "What to Expect Before You're Expecting" that there is approximately a 25-30% hazard for an 18-mid twenties girl to get pregnant each and every cycle. That drops to twenty-25% for early thirties, and 15-20% for 35, and sharply thereafter. It's particularly no longer a sure technology of path, so the ones numbers would differ. But sure, 18-22ish is the "ripest" of a long time to get pregnant...regrettably, so much females are not in a position via then.

People are getting bigger in general. Not nessesarily fatter, but just bigger, and 'vanity sizing' is starting to come into play. The clothes are bigger, but the size on the tag is smaller, to make people feel better about the size they wear. Also, they wore their shirts tight back then, that was just the style. It;s a combination of a few things.

I'm a small girl, and I have mens tshirts from the 70's that fit me quite nicely lol. They're a little big, obviously, but nowhere near as big as a mens medium would be now, you know what i mean? Just take the shirt over to show them.. it's not your fault it doesn't fit haha.

I must be missing something -

You asked why the difference in size as your question but then went on to explain your dad wanting you to wear it ...

If it doesn't fit just bring it over to show your step mom - share a memory from the past and have a laugh over the size ...

If you don't want to be bothered with it - tell your dad you washed it to wear it and the length of time it was stored must have had an ill effect because you washed it and it shredded (this happened to my jeans that I hadn't worn in 2 years).