If you think the current price of Bitcoin (at about $29,000) is expensive and you lost your chance to enter you're wrong. Bitcoin works as a store of value and it's replacing gold, so if we take the approximate total market cap of gold (about $9 trillion USD) and we divide it between $21 million Bitcoin (maximum possible amount) then we get a price per Bitcoin of approximately $43,000 USD. That's just the base price but it will keep rising because unlike gold this asset can't be mined beyond $21 million so there will always be more demand than supply.
So, as you can see you're still on time to start buying and holding. When will we arrive at the $43,000 price? I don't have math to support it but following the pulse of the market I can only guess it will happen in the next two to three years.