shouldn't je pense que trigger the subjunctive?

Justin, 

‘ penser que ‘ in a positive statement does not use the subjunctive form, even if there is a change in subject in the relative clause.

Also, in this specific example, there is no change of subject following ‘ penser que ‘ - the expression could be  ‘ je pense être prêt’, as used in the linked cycling article. 

There is a degree of ‘ rhyme and reason ‘ to the use of the subjunctive, but mostly ‘ why ‘ questions in grammar are a recipe for frustration. 

Some expressions always use the subjunctive, some never do - best just to learn them in context. 

The difficult ones are those where the choice of using the subjunctive or not changes the meaning/emphasis - they are the ones worth focussing on understanding why/when, and that is not always easy, as it can indeed be subjective. 

The links below may be useful :

 "Penser/trouver/savoir/croire/prétendre que" are followed with the indicative mood (L'Indicatif) in affirmative sentences BUT with the subjunctive mood (Le Subjonctif) in negative ones

 https://www.lawlessfrench.com/grammar/subjunctive/

 https://www.frenchtoday.com/blog/french-verb-conjugation/understanding-french-subjunctive/ 

https://www.directvelo.com/actualite/49388/theo-nicolas-je-pense-etre-pret