If I read it right, he is 27, tithes, and the 50% is gross not net. That is, he saves 33k (18+5.5+9.6) and earns 64-5-6.4=53. 33/53=61.5% and is a respectable 12.5 years from retirement! That's age 40.
In terms of the tithe, since you are tithing the full income right now, I assume you do not tithe again in retirement. Thus, I treat it like tax.
Second, yes you are understating long term expenses, but I would expect your income to increase dramatically even double in the next 5-8 years. You should be able to offset rent and mortgage costs with those raises, especially at the 17 year horizon.
Edited to add: the savings/net income is a rule of thumb, but the more important number is expenses in retirement. The rule of thumb assumes your expenses will stay the same. Since most retirees have lower transportation, clothing,restaurants but increased medical, this is reasonable. In your case, savings/(savings plus expenses) would look like 33/(33+30) if I include a rent allowance of 10k, which is back to your 50%. I didn't really follow the issue with your father, though. Also, marriage or kids will change things dramatically.