Start from what you know you are good at, pick one direction to test for 30 days and build a small routine around it. At 70 you bring something younger people cannot: decades of judgment, relationships and pattern recognition. Reinvention at this stage is less about proving yourself and more about choosing where that experience goes.
Keep the first test small and reversible. Mentor one person before launching a program. Write one essay before committing to a book. Volunteer one morning a week before joining a board. Small tests give you real information about what energizes you, without the pressure of getting it right the first time.
Accountability matters more than age. A weekly commitment to someone else, whether a group, a client or a coach, is what turns an idea into a lived routine.