Mentally I would say Xavier is in his 60s possibly close to 70 given that he did serve in the Korean war as I recall.
His clone body after becoming a brood was not crippled and likely younger.
Now he is in fantomex's body so physically probably late twenties or mid thirties.
But with all the deaths, rebirths (except mar-vell) and the sliding timeline, age no longer can be accurate
The age range for Korean War vets is between 84-87.
Yes, I really would prefer he be removed from that historical record.