Hi Gary
Welcome to The Business Travel Guru forum.
Yes unfortunatly Aeroplan miles expire after 7 years/84 months, from the date they were earnt, as per Aeroplan terms and conditions below:
9. Mileage in an account expires 7 years (84 months) after the date of
accumulation. Mileage accumulated in an account prior to January 1,
2007 is deemed to have an accumulation date of December 31, 2006
(regardless of the actual mileage accumulation date). Mileage may
expire without further notice.
Nice company policy, its fairly standard for any decent Company that looks after its employees. Anyway travelling 20 times a year into the US and Asia you won't have any problems reaching elite status. In most cases (for maximum return per $ spent), I recomend earning your miles on the short flights and burn them on the long flights. But in your case your company is paying and because you get to fly Business class if your flight is longer than 4 hours then earn them on the long flights and burn on the long flights.
To really maximize miles earnt then look at your routing, on the way to Asia stopping/transiting in another country, with a different flight number will in some cases increase the number of status credits earnt, which might go along way to getting to elite status quicker.