Everyone is obliged to attend Mass unless they are unable to for serious health [and/or] logistical reasons. The dispensation for elderly persons is not tied to age but to ability. Many persons older than 75 still attend Mass daily, let alone on the weekend, so age is not the issue.
When someone is confined to a nursing home, has lost mobility and other independent living qualities, they can no longer attend Mass and therefore have a dispensation from the obligation.
For many, the Eucharist is still available via the mission to the home bound which brings the Blessed Sacrament to their residence.
Our parish does an annual Mass for the elderly in conjunction with the nursing homes and assisted living facilities which coordinate transportation for these folks. It is always a grace-filled occasion.