It's never too late to get into Bitcoin, people said this when 1 BTC was worth 1000$ and now they regret not getting into it.

Bitcoin is expensive because there is high demand for it with a very limited supply. But don't worry, you don't have to buy a whole Bitcoin. You can buy 0.01 of Bitcoin at a time or 0.005 BTC or whatever that suits you. Fractions of bitcoin are called Satoshis and 1 BTC = 100 million Satoshis.

It's safe as long as you keep your private keys safe, as in:
Not giving it to people you don't trust, not letting people you don't trust access your computer if the keys are stored on it, Keeping your computer free of malware.
Public and private keys come in pairs, every public key has a private key. The public key is the address that you give other people to send you bitcoin and everyone can see your public key. While the private key serves as a "password" for the bitcoins you receive to the public key, in order to spend those bitcoins you have to use the private key.

I wasn't able to give an accurate explanation without getting into the technical details, I would have said that we actually give a hash of the public key to receive bitcoin but explaining what a hash is can't be done without getting too technical
I would actually like to hear from you on how to explain what is a private and a public key or we could both wait for someone to come and give a better explanation than mine.

No one controls bitcoin, it's a decentralized cryptocurrency and its price depends on supply and demand.
Investing in bitcoin is similar to investing in the stock market, if there is high demand for a certain stock the shares of that stock increase in their price. The same goes for bitcoin, when the demand for bitcoin is high its price increases and when the demand is low its price decreases.
As for the supply part, the total amount of bitcoins is limited to 21 million bitcoins, of those almost 17 millions are already in the market. The rest gradually enters the market through miners as an incentive for them.

Maybe add "Who are bitcoin miners?" or "What is bitcoin mining?" to the questions.

By the way, I've added your thread to my list, this way more people will be able to see it: List of Threads Giving Away Merits