How experienced are you in topping trees and installing antennas?

IMO the safest way for a heavy older person to climb and then top a tree is to have the right safety equipment, years of experience doing this kind of thing and some other experienced person to help.

Other than that, if you're willing to risk life and limb, at least hire an expert to assess your materials and proposition.

Oh, and if you really end doing this, try topping and attaching an antenna to a... say 8' tree first. That way you can learn the basics from simple maiming, instead of more severe outcomes.