A minimum starting age of 20 is arbitrary and strangely old for the setting, as even excluding fantasy fiction Alexander conquered the Maedi at only 16. I'd like to see an option to start at 16 since this is old enough to support all character creation options and (more importantly) the age characters stop being immortal.
For handling the focus/attribute points, either
1: Give 16 year olds no "free" points beyond their background (it's hard mode)
2: Give them no "free" attribute, but keep focus points
3: As above, but give them an extra focus point in exchange for losing the attribute (my preferred option)
3: Give one of the above and give characters under 20 a slight (smaller than one point) bonus to renown earned while they're under 20 (ala female player characters in original M&B/Warband).
For handling the focus/attribute points, either
1: Give 16 year olds no "free" points beyond their background (it's hard mode)
2: Give them no "free" attribute, but keep focus points
3: As above, but give them an extra focus point in exchange for losing the attribute (my preferred option)
3: Give one of the above and give characters under 20 a slight (smaller than one point) bonus to renown earned while they're under 20 (ala female player characters in original M&B/Warband).