Understanding that aggressive growth is one side of a highly volatile asset, what is considered volatile asset? Is it just not being diversified?

I have been reading this brilliant write up from u/McKoijion that beautifully breaks down high level investing. I included the write up below. I started reasoning, why would someone pick just VTI over using VT? And why someone would pick just VOO over VTI? My reasoning is (and this is my question, so please correct me) the less diversified a portfolio the more volatile it is. If an asset is volatile, it has the capacity for big losses but also big growth. I wanted to see what people thought of my reasoning. Right now I'm all in on VT and Chill, but if I was an old person with very little invested would it be wise to go all in on something like VOO?

The write up:
* VT represents all the stocks in the world. It has a 0.08% expense ratio. If you invest $10,000 in it, you pay $8 a year. I think of it like Vanguard total world.

* VTI represents all the stocks in the US. It has a 0.03% expense ratio. I think of it like Vanguard total US market.

* VXUS represents all the stocks in the world minus the US. It has a 0.08% expense ratio. I think of it as Vanguard except US.

* VOO is all the stocks in the S&P 500. It has a 0.03% expense ratio. I think of it like roman numeral V then OO for 500.

* SPY is all the stocks in the S&P 500 too. But it comes from a different company called State Street. It charges a 0.09% interest ratio. But there are other fees when trading, such as a bid-ask spread. This is when you sell your stock to a middleman for $10 and they sell your stock to someone else for $10.02. They pocket the 2 cent difference on every trade, and these costs really add up if you trade large amounts frequently. But if there are more buyers and sellers, they pocket less money. You sell your stock to them for $10, and they sell it to someone for $10.002. SPY is more like the latter situation. On a big trade, you might pay $20 in fees instead of $200. So if you trade more often, SPY is better. If you trade less often VOO is better.

Finally, you can combine different funds to make up other stuff. For example 60% VTI and 40% VXUS is about equal to 100% VT. A 70% large cap fund like VOO plus 20% in a mid cap fund like VO plus 10% in a small cap fund like VB is about equal to VTI.

If you want to optimize things, I suggest 60% VTI and 40% VXUS. Even easier is 100% VT. Even easier is a Vanguard target retirement date mutual fund that basically is 100% VT when you are young then adds bonds as you get older.

Some people like to overweight certain thing. You might overweight a certain country, a certain company size (large, mid, small, micro), a certain industry (tech, healthcare, etc.), or a certain stock (e.g., Ford). This is a lot more work though because you have to put your time and energy into picking good stocks/sectors. Plus, there is more luck involved in picking the right one at the right time. You can make more money, but often you can lose a lot of money.