What it says in the thread title.
I started running after a mere 22 year break in Feb this year and was soon ticking off races - 5 miles, 10K, and by August, a half marathon, which I ran in 1:56
At one stage, with advice from this forum, I realised I was doing too many hard training sessions, and cut right back to a long run, a tempo run and intervals - just 3 sessions a week, down from 5.
The HM was fine, and I took a week's rest before doing anything again. That anything was a humble park-run. Shortly after hte start, I felt my shoes slipping badly on a tarmac track - they're trail shoes and have no girp on wet tarmac. Some slips later, I felt a pain in my achilles tendon - AND SHOULD HAVE STOPPED RIGHT THERE...
but I carried on an finished in my slowest time of the year.
This was early August. The tendinitis was so bad that I was limping even when just walking very slowly, forcing me to cycle nearly everywhere. Early December and I am only just back to walking with no limp or soreness.
So, lessons learned:
1) Nearly 25 years is a long time! Don't let past performances influence training approaches even one jot after a come-back like this! (I easily ran 6 minute miles back then, even at the end of a triathlon.) Let those connective tissues adjust to training volume by just giving it time, even if your cardio-vascular system adjusts rapidly to training.
2) Don't change your shoes from neutrals to supportive a week before a half-marathon and expect to get away with it. If you're training in neutrals and managing fine, race in them, too.
3) Be aware that the stiff design of some heels can directly press on the tendon,, causing problems
4) Watch out for shoes with poor traction, as slipping about during a race is a way to get injured fast.
As I say, the tendon is much calmer now and walking is fine, but it's still stiff first thing in the morning. I think I'm now ready to head very carefully to the gym to do some eccentric calf exercises to see how that feels, and maybe do a very slow test run of just 500m to see if that brings back any pain on touching the tendon afterwards. It really is better to avoid getting this injury in the first place as it's going to take time to fully heal.
Have fun out there.