the best IT speciality for a 40 years old discharged military officer to learn

Question

• My career in the armed comes to end and I am in a transitioning period, I was a radio communication specialist with hardware experience only. Which IT specialty do you advise knowing that I am open to learn and want not to lose time with non adapted paths for my age. I mean a speciality in which fresher graduated and old reconversionist like me have the same chances.
• Thanks