What ever happened to Belters and Barbarians starting at 14...
You could still end up with a younger character using the companion rules.
Belter Background Package would bring you to 22 (so doesn't save you any time, but does add more than the standard number of skills) and the Spacer(Crew) career would give you a decent slew of appropriate skills. Of course in a Belter community you could as easily be a Medic, Administrator, Spacer(officer) or, if you liked Outland, Agent etc. Here you could make a time saving as it takes 3d6 years. You could exit both both those backgrounds at age 25 (but more normally in your early 30's) and begin adventuring (or start a conventional career term).
These packages are better than average due to the 3 optional steps at the end. These could raise any 3 skills by level 1 and add an additional 2 skills at level 1.
A 25 year old belter-agent created using the above could have:
Advocate 0,
Astrogation 0,
Carouse 1,
Deception 1,
Drive 0,
Electronics (comms) 1,
Electronics (sensors) 1,
Gun Combat 1,
Investigate 2,
Jack-of-All-Trades 2,
Mechanic 0,
Medic 0,
Melee 1,
Persuade 1,
Pilot(Small Craft) 1,
Profession (belter) 2,
Recon 1,
Science 0,
Stealth 1,
Streetwise 2,
Vacc Suit 1,
Rank 2 (field agent), Cr37500, Pistol, Vacc Suit, 3 Contacts (former informants or colleagues), plus one other benefit chosen from the list on page 22.
STR and EDU are reduced by 1 and INT and DEX are increased by one.
That is a fairly competent Belter Cop, easily capable of taking on the low level crime in his belter community. Even with the worst possible roll on 3d6 he'd only be 40 maximum but 33 is probably a more likely age, still a year away from any aging rolls. No nasty surprises either, you know exactly what you are getting.
Of course these are not limited to Belters and Barbarians, and you can't actually start adventuring before you are 22 but it still allows some solid skilled characters (especially those who rolled badly on their EDU).