Just as DLD says! If you have the option to try Cialis, go for it. Unfortunately where I live it still is a lot more expensive compared to Viagra. 100 mg of Viagra is a lot!
I can get a very good boner with 12,5 mg or so; I let the small piece dissolve under the tongue and it's in the system very quickly!
I'm also 30. The way of living matters a lot. Remember to do your Kegels (reverse ones too!), eat healthy and stay hydrated, water is the best for hydration.
How about adult entertainment, previous relatioships etc.? I also think there's a lot of psychological things behind the erection (well, naturally there are!), so you might think what kind of material you've viewed or what kind of sexual encounters you've had.
I notice from myself, very lately, that by myself I've gotten more lazy and getting a really good erection at times takes a bit of work. And orgasms by myself definitely are very different; could be I have the dopamine imbalance again for some reason, as quite often the release I have isn't so pleasing.
All in all, different kind of stimulus can be a key, but it's good to remember moderation.
I usually also go just once a day.
I hope you'll find the solution codename47, I'm sure an agent like yourself can do it! ;-)