Could not disagree more. Although when I was 18 I probably would have completely agreed.
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But hey, we each have our own games, so really, by that definition alone, we're both right
But what you are describing isn't intelligence, but knowledge. I admit that a person's knowledge changes (hopefully increasing) as they get older. But, their basic intelligence - learning capability goes nowhere but down after, I guess 25 (see below). So, having their basic bonus for RE & ME go from +0 to +5 as they get older, is counter to reality. (For the vast majority of us, there are mutants out here, thank [insert whatever you like to thank for good things here].)
The human brain does not reach full maturity until around age 25. Even then, there's no guarantee it has been honed to actually be functioning at full potential. That's just when the "hardware updates" are finally over.
But it very likely doesn't go from +1 to +8 in those few years, basically 800% better. Perhaps, 10-15% tops. A genius is recognized as such from an early age, and a person who starts out with an average intelligence will only be of average (or maybe, maybe very slightly higher) later in life.
The super-jocks out in the professional grown-up world were super-jocks in middle school - especially compared to the other kids. No, they weren't as big as they would become, but they showed what they would become early-on. Except, in rare cases, it is easy to see who will be and who won't be strong, smart, charismatic at an early age. (Some scientists claiming you are pretty-well set by age 5, I will go ahead and be more conservative than that, and go with puberty ~13. That is not saying you are as strong as you are going to be at age 13, just that is easy to see that you are going to be strong, by that age, as you are likely larger in some way than other kids your age.)
But, in the cases of the PCs, who are universally starting there careers in the late teens, sometimes early 20's if you are a mage and took a TP that had a long training time, then who you are going to grow into and who you are now (in a purely basic, non-skilled sense) are very close. Not knowledge, not experience, but basics. Those basics will get "fine-tuned" but they will not alter greatly unless....magic, technology, injury, whatever. So, having such a huge difference in stats at character beginning is not very realistic. (Except maybe Wisdom, which I think is better served as an experience/learned thing than basic attribute - though a talent can represent the fact that this youngster is wiser than others at their age.)
Of course, having that 98 lbs. weakling go through the strength training montage and come out a much stronger individual can be fun to play (just remember the montage music). But that is not the norm. The norm is that the 98 lbs. weakling just becomes the 130 lbs., fatter weakling - provided he lives long enough.
Basically, I agree that there can be some difference, just not the difference reflected in going from a 50 to 78, or a 60 to 90. So, maybe it should only be there for those exceptional/special stats that are part of the character's uniqueness. Like have the player take a talent to reflect that he can attain an exceptional strength (or whatever). But to nit-pick him going from a
base Strength bonus of +5 to a +7 (Can you tell I am more used to playing RMSS/FRP?) is unnecessary. In RM2/C I guess going from a +5 to +10 is more noticeable, so I can totally see wanting to have that in there, though still not necessary - just give them enough stat points to pick their total stats and if they want to be able to increase any, make them spend talent points (or picks). This would mean giving them more points to spend on stats (gasp!), of course.