...... That's movie continuity vs comic continuity. Its not the same thing....Do you really want a 20 year (at least) age gap between Scott and Alex and it being said they're brothers when Alex is old enough to be his father (yet doesn't look it) sorry that's very very lazy and a bigger mess of an already horribly messy movie continuity.
Id personally rather Alex just be Scott's father in the movie universe and call it a day..... The Alex and Scott relationship due to the age gap already wouldn't be the same as the books so there's no point trying to force it
Even with a big age gap, it's still possible for Alex and Scott to be brothers. I know a woman at work who is part of a large family where there is more than 30 years' difference between the youngest and oldest children.
The age difference depends how old Alex is supposed to be in First Class, how old Cyclops is supposed to be in the original trilogy and when the original trilogy takes place.
The original trilogy can't be way into the future because it began with a wartime scene set in 1944, in which Magneto was aged about 10 (I would guess).
The actor playing young Erik in X-Men (2000) was aged 12 when that scene was shot, and the actor playing young Erik in First Class was 15 when the scene was re-created for that movie (the same age as the actor who played young Xavier, whose age is definitively credited as 12). The character looked to be aged 10-14 at most.
I would say Magneto in the original trilogy was in his 60s and not any older (no way he could be in his 70s). If Magneto was 10 in 1944, then 50 years later (in 1994) he would be 60 - and 60 years later (in 2004) he would be 70. On that basis, the original trilogy likely takes place sometime between 1994 and 2004. You can see the Twin Towers in X1 and if you take that into account, the first film can't be later than 2001.
If we bear in mind Origins, a version of the 1979 Three-Mile Island incident takes place at the end of the movie and Wolverine has been on the road without a memory for 15 years, making it 1994. If we theorise that the Three-Mile Island incident had already taken place, making the location a prime spot for Styker to set up a base and go undetected, then the end of Origins could be, say, five years after 1979. Thus it would be in 1984 and X1 is then in 1999.
My brain is fried now so if someone can factor in Cyclops to all that, we can see where that leaves us.