We can talk about work life balance, choice/nature of work, hours (full time vs part time), type of company/team you prefer etc.
If you think 35 qualifies you as an old timer, I think you might be operating in a bubble. Unless you’re retiring early, you’re not even halfway through your career.
If 35 makes you feel like the “old timer” in your workplace then that might benefit from trying some workplaces where 35 still makes you feel like one of the less experienced engineers.
As for ideal workplace: It’s not actually that different than what I wanted when I was younger. Work/life balance, good communication, and reasonable workload are universal wins at every age.
The only real difference is that as I get older I have less tolerance for negative workplace practices and more confidence to speak out against them.
The point is that you shouldn’t look around and see yourself as the exception due to age.
The more age factors into the workplace, the worse it will be for you.
A mix of veterans and rookies is a good way to encourage a mix of old and new ideas, and also enough questions being asked (and people explaining to each other how things are supposed to work). I do worry a bit about onboarding of rookies into workplaces when it's all WFH; you can always ask for help but it's not as good as having a person sitting at the desk next to you.
Large or small companies both have their advantages, but small companies are more likely to allow a variety of tasks to be done by the same person; employees at large organizations are more specialized.