It's good you have a mentor and hopefully you'll have access to more guidance and training as you go along.
The National Governance Association considers someone a 'Young Governor' if they're younger than 40 and run a termly group that can be joined by governors whether or not their school has a NGA membership. Their stats a year or so back had more governors over 80 than under 30, and a decline in those under 40 to roughly 6% of governors so the boundary for young might rise as the demographics change.
Where I am, they advertise being a governor with how it helps CVs - it does give a lot to talk about as I find for most interview style questions, there is something from it relatable, though I think that advertising is more aimed at mothers who have a gap or people who want to shift into education or working in related areas. It may be helpful for you, though I'm not sure if it will as much with your significant experience already - I think it will be a great addition to most schools!
How it will work really depends on the school. Some schools have committees, some don't - school I'm at has never had committees, has always been the circle model until this year when the trust is now requiring us to have one for pay (before we had a pay panel instead), but no others.
Policies and how feedback about them is organised is a common issue - some will ask for feedback before the meeting and some at the meeting, some will respond before/during/after, some you'll only see if feedback was taken on board when the policy comes back the next time, some policies governors may not get any say, not even able to vote no,, just confirm they've read it - typically ones standardised either by the trust or by the council that one can at most send feedback through the chair that is very difficult to get much other than typos changed (I've been trying on one of these for nearly 4 years, even though the area head at the trust agreed with me, it still hasn't been done) -- and this can change over time as staff changes or whether anyone has chosen to vote no there tends to be more feedback given.
One thing I recommend if available is some schools have briefing with other schools in the area or in the trust where we're updated on legislature and issues that we can look into in our link visits or with our board, can talk with people from other boards about practice and issues, and it's a great way to get wider insight.