Instead of focussing on “delaying ageing” focus on timelessness.
Be present in the moment, be aware of the mass-consciousness belief about time and death and constantly put forward your own desires for your body/mind etc.
Having a strong purpose for wanting to be alive, something to accomplish perhaps that would take longer than a regular human life span may help.
If the predominant feeling is fear of ageing/death then that’s what you will experience, to go beyond that you are going to need to think very differently than the norm, and you’re going to need to be a more active conscious participant in your own creation.
There is a wonderful book titled “Anna the Grandmother of Jesus” which may give you inspiration and a starting place as the title character/person in the book (and others within the same community) achieved great lifespans.
Granted they came from a strong tradition and communities where ancient wisdom was preserved but anything is possible, and we’re entering into a new era where it’s going to become easier to go beyond what has previously been possible.