I have written about why it would be accessable to everyone immediately before. The TL;DR is that it's more profitable to make everyone immortal than it is to still allow people to die.

• Governments worldwide would save on paying out pensions

• Governments would save out on healthcare costs of treating age related diseases

• Governments would have an eternal tax base for every extra immortal person

• Insurances will have to pay fewer payouts during the expensive last years of people's lives while continuing to receive profitable monthly payments forever

• Businesses won't have to pay into retirement funds anymore

• Businesses won't lose valuable worker experience and human capital to aging anymore

• Businesses will generate an eternal consumer base for every immortal person, a dead person can't buy your products

• Banks will be able to give even higher loans and mortgages that take centuries to be paid off due to immortality, immortality might even be sold with a 500 year mortgage attached to it

These effects combined will mean that everyone in society will push to ensure everyone will immediately become immortal once the technology is reached. Not for some sort of altruistic goal. But simply because it's the most profitable action for everyone involved.