Local club to you that has a veterans team (over 35) may well be best starting point.
Although most will be narled old p#@sheads who only remember the laws from the 1980s however usually good fun to play and socialize in.
A large rugby community in Somerset so should be something near you.
Loads of older people play on down the Leagues. Especially 2nd team downwards. Sometimes Clubs are desperate to make up the numbers. And as well as age they say our game is for all shapes and sizes too.
The +35 teams that duncanb mentions are, in my experience, filled with people who have played the game their entire lives.
The problem they face is they do not have the stamina, strenght, speed, reflexes and endurance.
They problem you would face, is that besides all of that, you will not have the technique. How to tackle and how to receive a tackle is something that takes years to master.
After 20 years of experience (most of the +35 have that) you quite aware of what you are able to do, and what you are not. Tackling is not an instinctive movement, that's why it's very important to learn it young. learning how to be tackled is easier but there's still some learning curve there.
Most of those 35 year olds have been training 2/3 times a week for decades, through rain and mud. There's a lot of muscle memory involved.
An average 44 year old tackling someone for the first time in his life is a considerable risk. There's a head/shoulder placement issue that is instinctive for players who have played since they were young, but that can hurt you pretty bad if you do it the wrong way at that age.
Some will tell you you can learn that. Takes a long time in my experience. These are split-second decisions that again, come intuitively to every single player you've ever watched.... cause they started playing very, very young.
You can try and get away it, sure. I just think the risk is high.
Have you thought about playing tag? Just to see if you can keep up and to get used to the tempo, ball, etc.