Minimum age is 30 for triathlon and there will be 5-year age groups. There will be no GB selection races as its based on individual entry and individual competition rather than representing a country.
However, for all purposes its country based. The last games in Melbourne Australia had 25000 competitors.
Of course, if you enter the Triathlon you can also enter other sports such as athletics inc. half marathon and cross country, there are also road and track cycling races!
The official web site is here: