More Draenor-born Draenei? This pleases me!
But do recall that a "40 year old" in mindset does not translate well into Draenei behavior. Rather than say 'My draenei is 40 years old if he's a human' translate the signs of age into something that's usable for a draenei regardless of how old he is. Try this:
In human years, 40 is roughly one's prime time. In today's industrial society, a 40 year would: have likely finished college by now and have started working long ago; been at a career long enough to have good experience; have earned enough to be fairy financially comfortable stable; are getting married or have married/a long-term relationship with possibly children, which can range from babies to teens just about to reach adulthood. There usually is no mid-life crisis at this point--the individual would have
just entered the dreaded 40s, though there are some who feel the 40s are the new 30s (especially today). Physically speaking, reproductive abilities have not yet taken a nose-dive, but the male may not be as well a performer (starting or main show

) and the female's ability to bear children may be less ideal (or healthy) as she would have been 10 years ago. Menopause and climacteric (for both genders) usually do not come in until at least a couple years, and while it's possible for that age, it'd be unusual (and socially decidedly unfortunate).
Perhaps the best way to RP your draenei as a 40 year old, if born on Draenor, is to establish his personal experience that could take a toll on his body. Perhaps he got physical way too often. Maybe he drank or used some sort of drugs way too often (Lord knows frequent party-goers seems to age twice as normal). Perhaps war and other stressors in his life beyond the draenei purge and crash took a toll in his body.
TLDR: try not to decide how to age your draenei chronologically. Instead, consider psychology, physical ability (not just in sex, but all aspects of life), and life experiences that contribute what would age a draenei. Do note that physical 'aging' is not normal of draenei, so others, regardless of age, may react with sorrow to see your draenei looking so old and not being Velen.
Here's a sample on what I do with my draenei: Two out of three of my goats, Kapre and Diwaata, are 306 years old, and both are born and raised in Draenor. However, I RP them like they're in their mid-20's due to how life treated them in those 306 years: they have only started obtaining stable relationships, only beginning their careers, but would have had enough life experience to display wisdom and cultural establishment. Compare to my night elf, 315--only 9 years older, but I RP him like a budding teenager due to being stuck in the Emerald Dream almost all his life, being a lazy bum of a druid who just wants to play in the trees. sing, and play his lute.