Assume all programs use redshirts/grayshirts at about the same rate, and that they recruit players from HS and JC at about the same rate. Also assume all missions result in a two year absence.

Calculate the percentage of RMs on BYU's roster that actually play a significant amount of time, ie, scout team members and garbage time players don't count.

If the RM proportion is:
100%, then we have a two year advantage;
75%, then we have an 18 month advantage;
50% gives a one year advantage;
25%, then a 6 month advange;
0%, and there is no age advantage;

Everything else can be interpolated from there.

Thus, it all depends on the BYU RM percentage of players who actually contribute.

It can also be argued, as others have repeatedly, what the age advantage actually means. I think of an RM as someone coming off a severe injury that needs up to a year of conditioning and rehab. Bronco believes there is an advantage, but it is with mental and emotional maturity. Lavell thought the plusses and minusses cancelled each other out.

One negative often overlooked is the break in team chemistry and continuity when a key player leaves for a mission. This is more of an issue in basketball than football.

It is a non-issue as far as on-the-field performance is concerned, IMO.