I got my PhD in 1977 at age 35. I turned down temporary job posibilities at Columbia, UNC and other schools to go to UGA in Georgia, because I had a family and wanted a tenure track job. This was perhaps rash, as I was "buried" there away from centers of research in my field and ahd to struggle to get out and be noticed.
In 1979, at PhD age 2, age 37, I gave my first talk, at an international conference in Angers France, before an international audience. I prepared for weeks. It went well. From that moment on, I had a large number of international connections, invitations, and potential jobs.
I recommend giving talks as often as possible, for the experience and for the exposure. I.e. never turn down an invitatioin to give a talk, and when you go to a conference uninvited, have a talk ready.
For years, everywhere I went, invited or not, I was either asked to speak after arriving, or asked if i wished to speak. Once I entered a room late where talks were being discussed. My name was on the board for some reason unknown to me. Then the moderator said "we have been voting on who we want to hear, you are speaking on Friday." I had to go to my room and quickly prepare a talk since i had violated my rule of always having a talk ready for every conference.
Another time i arrived for a semester long stay at an institute and as I arrived the first day to find my office, an organizer spotted me and said "this is the guy i wanted to see. Will you speak first this semester? We begin Thursday." Again i had to go prepare a talk in a hurry. These quickly prepared talks are not at all ideal.
Since the first one, I have given over 60 talks, the latest in 2001. I have been invited to speak in Italy and Spain twice in the last 6 years, but been obliged to decline for health reasons.
The stimulus of having to give espeically an international or national talk, or les so even a seminar talk, is very energizing. Even when I have given what felt like a mediocre talk on work that was not mature, the stimulation has always led to finishing the work afterward. So the talk always benefited me if not thE audience SO MUCH.
It can be nerve wracking though to have to speak in front of a crowd of experts. But mostly they are very nice.
Basic rules I recall:
prepare thoroughly. Practice actually giving the talk in advance to a live audience, to practice the timing and anticipate problems. this is the most useful thing.
when speaking try to identify some friendly face in the audience to talk to. In general speak to the people in the room instead of reading the talk, or giving a canned speech.
dont be afraid of them. they want to learn from you, give them what you have, and if you can also make it clear and understandable, they will appreciate it.
smile, enjoy yourself.
and quit on time. once however i was too strict about this, and quit before making my main point. my timing was off because they had dawdled about starting. it was a laid back group, and i should have asked if i could have 5 more minutes and ended well.