One hopes that we are not in a situation where the IA is explaining to the actuary "mathcing assets and liabilities". That should be your expertise. In general, matching or immunization works best when the group is large (duh, general actuarial priniciples). That does not exclude it from this situation, but caution is advised, especially since (it appears from your plan specs) the actual retirement age can impact the plan's liability. Might be prudent to mention that to the plan sponsor and/or the IA.
BTW, does this IA expect to reap some commission on any immunizing transaction?