Why I can not watch adult websites on my iPhone date ,And I’m 38 can someone help me

The setting on your phone that would prevent that is at Settings > Screen Time > Content & Privacy Restrictions > Web Content. This should be set to Unrestricted.

Also if you have a Content Blocker installed at Settings > Safari > Extensions, then that may be preventing access.

If those 2 locations are not the issue, then it is not your iPhone that is blocking the content.

iOS doesn’t care.

Whatever added web services or DNS services have been installed or configured might block access.

Or the folks that manage the Wi-Fi network you are using can block websites, as well.

There might be carrier services for this too, check with your carrier.

Some repressive governments can have laws that can either make access more difficult, or can lead to providers simply not serving that content to residents of those areas, as well.