Hi,
If it’s remaining erect on direct stimulation, I don’t think there’s much to be worried about. I’ll suggest getting your blood pressure checked and also blood sugar to rule out the possibility of hypertension and diabetes as these are 2 common culprits in causing the erectile problems. However, I don’t think it’s any serious problem and you can always ask your partner to directly stimulate your penis and then you can have sexual intercourse. I sincerely hope that helps. Take care.
This could be a age related problem. I am 50 and I have the same issues that were not there a few years ago. I've heard that men app. my age need direct stimulation to maintain their erections. I personally have an issue with my penis going soft while in side my partner and also the inability to ejaculate with my partner. This is new also for me within the last few years. However, I do not have a problem with ejaculating during masturbation if I am doing the masturbation. So, I sympathize with you,but I do not have a solution except that you may want to look into Viagra or similar drugs. With these drugs I can maintain the erection, though they do not help with the lack of ejaculation problem.