The age at which you will fly a certain type of aircraft depends on many factors. If you get hired as pilot with a regional carrier, do not expect to become a 777 F/O at age 26... unless they start operating that type between Gatwick and Birmingham. But you might definitely be a CRJ captain at that age. Most airlines give promotions by seniority (being date of hire).
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I had a friend joining KLM right around 1970, his initial position was DC-9 F/O, but he hated short haul flights, and eventually got promoted to DC-10 F/O about 1 or 2 years later... his age was about 25, and that was a "heavy" and "long haul airplane" as "age" seems to impress many here. He then became DC-10 captain, about 1980, and when KLM got MD-11s, he went on that type. No need to say how highly experienced he was on DC-10/MD-11 types, finally as a TRE-TRI.
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I flew a 6 month contract with Cargolux in the early 1990s, 747-200. I recall having a few F/Os who were maybe as young as say age 23 or 24 flying a "long haul 747" at their age. As impressive as a 777 at age 26... To my opinion, the "size" of an aircraft does not matter. It does not take much more muscles to handle a 747, than piloting a CRJ. And as far as I am concerned, the 747 is much more stable to handle...
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Yes, in USA, still takes years to fly long haul aircraft, as pilots have a salary index based on aircraft gross weight. Do not forget, for the FAA/ATPL you need to be 23 of age, and the large airlines, AA, DL, UA prefer candidates with a college degree. That brings minimum ages up.
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The Pprune culture is the teen "I want to be a 380 captain" generation. As your voices are so loud, learn instead, to listen to old farts and their recommendations. We want you kids to acquire maturity and education first to be airline pilots, not kids crying for a new toy. I was quite succesful as an airline pilot instructor, but change diapers was not in my job description.
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Happy contrails