ladytina42, I retired at your age and I'm a loner too. I've never regretted it. I don't miss teaching and I've lost all interest in returning. It's a very enjoyable second childhood.
Don't even think about 'replacing' work yet, instead, think in terms of recharging your batteries. Give yourself time.
Follow or try hobbies and interests, reflect on what your work prevented you doing in the past, (it's time to catch up) read a few books, listen to music.
Don't dive straight in to study, volunteering or socialising just because other people do. You have the golden opportunity to do things in the most pleasurable way, (your way) not the most efficient.
I've had to fight against the feeling that I should 'make myself useful' (instilled in childhood) and choose, instead, to follow my own moods and inclinations - it's wonderful!