As a 40-something, I survived being a born again biker and I'd like to offer these thoughts to anyone thinking of doing the same.
1. Biking is still huge fun! So it's well worth doing.
2. The roads are busier - You don't notice in a car, but once on a bike you realise how very much more traffic there is than you remember, and you'll find cars faster than you remember too - but with just as little awareness of what's around them and just as little effort spent looking out to avoid hitting you.
3. Roads have changed - They are now covered in unnecessary white paint. There are huge arrows showing you which direction is straight on at every junction, and huge circles reminding you of the speed limit - as if the signs every 50 yards might have escaped your attention. The point is these are all very slippery when wet!
4. Bikes have changed - This is particulalry noticeable with sport bikes, which are unbelievably faster than you remember - so much so that the single main cause of bike accidents is now bikers taking corners too fast and crashing.
So - what to do?
Start slow. I bought a "slow" 650 cruiser and learned to ride again. I hadn't realised how much I had forgotten - like road position and counter steering. I was terrified it would rain and fearful of the debris that builds up in the centre of country roads. I rode defensively and timidly, hugging the side of the road. I was having fun, but it was laced with big cold dollops of fear.
Get training. Then I went on a Bike Safe day in London with the Police. Good talks from real bikers, good discussion and good biscuits. Then we had two 40 mile observed rides thrown in. 40 miles with your own personal police bike 18 feet behind you is completely nerve wracking! Mine was friendliness itself and very helpful in his observations, showing me better lines of approach to corners, how to take a safe but more dominating position on the road and when to go faster. Riding home afterwards was such a relief not to have someone following me, my confidence increased enormously.
I also bought and read the Police handbook on their "system" for riding - which was excellent.
Enjoy yourself. Riding was always a skill. Skills rust - so you have to shine your up again before you can ride like you did. This might take months, but it's worth doing.
I am having fun, I am riding more and I am riding safer.
I hope you will too.